Here is some of my feedback so far. All of it assumes the user is using Revit:
I would improve the starting environment in two ways. The general environment can easily be improved, but this is more of a philosophical question. What environment do we want to be in in VR? should it be reminiscent of an architect studio or represent the new possibilities of VR with semi impossible architecture? I would go halfway, maybe a sleek floating table that fits the general size of the model.
On a more utilitarian note, I would add patterns, texture or grids onto the white walls of the environment. When I used it, there were many instances where the background was completely white with a single tone. This removed any point of spatial reference, which can cause nausea if the model is being moved around and the user loses stable points of visual reference.
I see 'waves' in the model. I have a feeling it is because of the limitations of the graphic card since our model is huge (25+ million triangles). Perhaps the performance would increase if we could disable the screen preview. If so, add an option to disable the 2D screen viewer. Perhaps there are other adaptive performance settings that can be tweaked or you could even simplify the model geometry.
I would add an option to see general statistics about the model: number of triangles & number of texture maps. This will make people "triangle aware" so they can make the correlation between heavy models and slow performance. It will also make troubleshooting more easy since Revit does not have a triangle counter.
I would add a cursor for users in the real world to point thing out for users in VR. The communication with someone in VR is always difficult and this would be an easy way to help solve it.
Consider adding an option for section cuts that are only orthogonal. Autodesk has something like this in their BIM 360 services (Design, Team, Doc, etc). Alternatively, the section slicer could align with the Revit grids, but no other angles.
I like sections where the lighting is not affected by the section. I would suggest adding this as an option.
Here are some examples:
This would allow users to do sections and analyses the solar effect on a particular floor rather than having the light penetrate where there should be a floor, ceiling or roof above.
I would make the time and date toggles much bigger. I would also make the scroll bar much longer so that it is easy to do small movements of the time and date with our hands. Perhaps when you select it it becomes much large than the menu or there is a button to 'pop out' a time and date slider. Another alternative is to do like Enscape does and have a button that allows you to drag the sun.
Generally a lot of the toggles are small and require precision aiming. The scroll bar on the right is one of the most problematic. I would consider a system like the Oculus Medium menu uses where pressing a particular button allows you to scroll up and down instead of trying to catch and hold a button. Allowing the thumb sticks to scrolls could also work.
I would consider allowing users to use 'view templates' that exist in Revit. This will turn things on and off, create color overrides and transparencies for certain families. For example, a plumbing view template could make everything other than plumbing grey and transparent. This is an easy way to do very task specific verification in VR without trying to control all of it in VR.
In a similar vein, allow users to use an Xray mode for a particular layer or category. With the plumbing example again, allow users to focus a single layer or family type that they can see through the walls. This can be useful if there are no view templates or the user is trying to isolate a Sketchup layer or layers for analysis.
Teleporting to the top of a rood is hard. Our building has 32+ stories and users were not able to teleport to the top of a roof. Other times they would teleport on a tiny 5 inch ledge of the building, creating vertigo situation. You otherwise have one of the best teleport systems in the industry so far.
Some of the movement buttons are not labelled in VR. Doing so would help users understand how to move faster. Enscape has a cool system where the button IDs only appear when you look at your controller. Perhaps these less important icons only appear after staring at the controller for 3-5 seconds.
For clients, I would allow the designer to disable the artificial movement buttons. We tell clients to not use these, they use these and immediately get sick. Sometimes they also use them by accident and get sick.
I would dedicate a button to going into model mode (dollhouse mode). When users need to explore many levels and roofs on a tall building, it is the easiest way to get around. Older users needed a lot of guidance with using buttons that were not physical (left hand panel buttons).
I would put some attention on allowing users to leave voice comments. I believe IBM has a service that transforms voice into text. pointing, taking and moving on gives a very smooth VR review experience.
I would allow users to Shit+Select or Ctrl+Select view to add or delete them from the experience. Right now I have over 150 3D views and I have to uncheck them on by one. Perhaps a Select All or Deselect All button would be helpful as well. Otherwise, start with ll views un-selected.
Please allow us to export our 3D sketches into Revit. This can be very useful for concepts.
Please allow use to sketch in model mode (when the model is not in human scale mode). This is the most important for concept reviews.
Allow us to place loaded Revit families into our model.
The sections with backface culling are problematic for Revit models. We don't get a sense of the thickness of the floor slabs. They appear infinitely thin. Probably the best solution is to fill any cut section of a closed polygon with black or dark grey, much like we do in architectural sections.
Allow users to walk through walls somehow. Enscape uses the walk/fly dichotomy, but I have gotten stuck in rooms with no doors before due the teleporting after a section. With limited workspace, it is hard to just walk through the wall and teleport.
Consider adding a mini-map above the left hand menu. One of our older users got lost very quickly when teleporting. Perhaps clicking on the map teleports you there.
The following comments are more important.
Consider linking your comments into the BIM 360/Forge infrastructure from Autodesk. This way comments become part of the workflow infrastructure and can get responses and proper archival.
Consider providing light baking for a premium cost or allowing users o bake the lighting locally. This will increase performance, but mostly allow us to see exactly what the space will look like. Light baking needs to be paired with adaptive exposure. I can help you achiever this if you require assistance, it is one of my specialties and personal priorities.
Feel free to ask for clarification on any of these suggestions.