Just to clarify: not loops, as in the general term used in modeling, but loops, as in the term used by bmesh to describe per face per vertex.
Link seems to be dead; I presume it uses approximation like zbrush. But it will definitely cause problems because aside from simplify brush
collapse and subdivision collapse methods also create the risk of breaking blending and vertex resolution
Fixed the link. If you are conscious about the current dynamic subdivision the brush will subdivide to, you should have no problem.
I would argue that we should leave the per-face painting as is and add an option to apply vertex colors to all selected vertices.
Also, it would be nice to have more vertex color channel slots for use with the render engines (as it is an easy way to create complex material blending setups and you can easily hit the limit).
Iām not sure how easy it will be to have per face painting and support on multires / subsurf.
Support of multires, excellent performance on millions of faces, this is a must to have.
If not, letās forget the whole thing.
BTW, about what support of multires are we talking about, it looks like a dead horse alright.
The trick would be on how you would allow the ability to use vertex painting on data created by the modifier stack (which can be changed or deleted at will). Then the trick would be making it fast enough to be worth using on a multires sculpt.
I canāt imagine this being a small project.
Iād rather not have mr andrew waste time on this, without a proper multires modifier/workflow vertex painting, masking, even texture painting (on realistic assets) is kinda broken. On the other handā¦ speed for texture painting is MUCH more needed, if you ask me, as well as mirror.
Sorry, staying purely on topic and answering the question: Better vertex painting speed could help, I wouldnāt matter if its per face or per vertex, but it is hardly important I believe, only nice as a small plus when other important things are done.
Please excuse my ignorance.
How I can see-preview two or three Vpaint sets (layers) in GLSL mode? How to mix them?
I do miss something here, do I?
In cycles render preview, of course I can. But not my point.
I even managed (LOL) to import two or three huge meshes from ZBrush (GoB) and select deferent zb-Vpaint sets on one object (via Data Transfer Modifier). Oh yeah. Great. (how complicated UI is this, please feel free to express your opinions on this)
However, all these have to be reviewed by developers before we go deeper on this.
Multires/subsurf, GLSL preview, etc etc
Please do not remove the ability to specify vertex colors per face. It is very useful for game development. Heres an example of using it to create untextures models:
If work is done on the vertex painting system it should be on more tools like layers, improved color picking, color adjustment, and color replacement.
Attachments
I use vertex paint per-face a lot, itās really useful. Itād be a significant loss for me/my time if I couldnāt do that anymore. Iād like performance improvements, but not at the cost of per-face painting.
I didnāt even realise that you can vertex paint in a per-face mode. I know about the face selection masking, but how do I paint per face? I canāt find anything about it in the documentation, so I am clearly missing something obvious 
Coming from a 3ds max background. The vertex color channels are only uvwz channels (RGBA).
What I would love to see is vertex colors done the same way, then the user can map them to be per face, or per vertex, it doesnt matter
Also having the ability to edit the vertex colors in the uv editor is super handy for game dev!! Also would be good to have vertex color set-able in the regular edit-mode, even if it just on a basic level. Again, like 3ds maxā¦
I havent read the rest of the thread but yesā¦ we use vertex painting a lot for quick masks to help variation on large landscapes.
per vertex per face is extremely usefulā¦ I wish the attribute node in cycles could access itā¦ would be great to use in cycles node shaders for masking. Itās something i do a lot in BI nodes and itās limiting that vertex groups canāt do it!
That said itās also highly desirable and conspicuously absent from multires data. itād be great to be able to paint on multires verts.
given the different use cases for mutires and from a performance POV itād be fine to be per vertex But Iād sorely miss it from standard meshes per face
At the risk of repeating myself, can someone please enlighten me how to activate vertex painting per face?
please keep both. per vertex is great for blending while per face makes it easy to create hard edges for abrupt changes.