Btw. parallax mapping is already declining, all the hype is on tesselation now...
That also has it's own set of caveats. But hey, it's always a compromise when doing realtime stuff I guess.
To be honest, popper artist authored normal maps would go a long way already.
Worst thing Trem can do imo is to add phong or blinn to everything, without redoing the assets to work with them.
It's also not as simple as people like to think...
When you add bumpmapping in the best case your texture memory consumption doubles, but usually it's much more.
Color textures can be compressed with a 1/6 or 1/8 ratio and it looks fine mostly, but when you do it on normalmaps it turns into a pixelly mess. So either you use something like 3dc which halves the memory for them, but that's not supported on older gpus. So you can decide to limit their size, but it's still kind of stupid since you're thrown back half a decade in terms of texture resolution. Then you need to make sure the lightmapping works with it, which means rewriting stuff in the editor, engine and compiler. And unless you make everything realtime it's going to triple memory consumption for lightmaps. Making it realtime wouldn't work well mostly for people with older hardware.
If you add speculars to the bumpmaps things really start to get out of hand, all the textures which looked fine in the fixed function renderer suddenly show their age much more, because 128² textures tend to look fine when all you have is vertex diffuse lighting and bilinear filtering. When you add per pixel specular, it just looks awful most of the time. So for it to get up to todays standards you need to redo most of the texturing in high resolution, on top of the massive increase in texture memory. And that's not only problematic from a rendering point of view, but download sizes increase, artist time increases, internet bandwidth and server costs become more expensive.
And if you want to do pretty phong or blinn style speculars you quickly need color specmaps and a glossiness map.
Ofcourse then you run into the issue of shader aliasing which cannot be resolved with msaa. Plus it's kind of silly to have all pixel perfect geometry without players casting shadows. So you need shadowmapping and all. But that also has gameplay implications (e.g. you can see the shadow of the lisk sneaking up behind you, unless you have it turned off). You can ofcourse make the shadows only cast right down, kind of a improved blob shadow kind of thing.
But how viable is all that stuff when you're working with a renderer that is still stuck in 1999?
What I'm trying to say is, it's a slippery slope, every change has implications where you wouldn't expect them.
And going from fixed function rendering to per pixel lighting isn't as easy as people like to think.