Seems like a lot of what have been traditionally rack-mounted gear has now gradually transitioned on to the pedal board, and amp heads have now become smaller due to class D. Cabinets are getting lighter too. I more than enjoy seeing our equipment get lighter and smaller, but I still enjoy the aesthetics and the modularity of a rack-mounted system. Can there be a compromise? Maybe a 1/2U rack-mounted system? Many things like power conditioners, compressors, tuners, amp heads, pre-amps, power amps, etc...can probably be down-sided to 1/2U with our current state of technology, or perhaps converted into some sort of 500 series module that we could integrate into a 500 series/power amp hybrid system? Maybe this is all a pipe dream, but I love the idea of having a rig with the flexibility of a rack-mounted system, but shrunk to the size and portability of a lunchbox. I hope I am not the only one here that dreams of this sort of thing.
There have been quite a few threads on this over the years on TB. I built a DIY preamp/power amp rig in 1/2 rack format several years ago, but I'd pretty much need to DIY the vertical 1/2 width rack too unless something new has come along recently. I'm likely to just go back to using a standard rack size amp if I ever go back to gigging, although I could just end up side by side mounting the modular pieces, which I built with that possibility in mind.
Interesting idea. Closest I can think of is the now-discontinued Markbass MoMark line. I don't think it sold very well or for very long. I don't know if Markbass made their chassis spec available for any other manufacturer to make compatible modules. MARKBASS | Products | MoMark SA 500 I think the problem is having a standard chassis that accommodates speaker output and not just patch I/O connectivity. Standardizing would mean there would have to be industry agreement on what ins and outs should be included and how they should be rated. That and also safety and UL listings needed. 1U only provides 2 horizontal slots, so a preamp and a power amp. Current designs probably aren't spec'ed to sustain the higher current needs of a power amp module. 2U would give you 4 horizontal slots, preamp + power amp and 2 effects. I haven't seen these on the market. 3U is the standard 500 series chassis for 6, 8 or 10 vertical slots. But I believe that the real barrier is just how expensive 500 series equipment is. You can buy a decent new bass amplifier for the cost of the chassis alone.
On a tangential note, check out this little pedalboard amp I saw at NAMM in January: Stereo Amplifier Module A few of us bugged them about doing a higher powered version, seems like 300 watts might be about the sweet spot. They have a nice variety of cool modules, and I thought the whole thing was pretty clever and very well executed.