Weak is a relative term, I apologize.
My real point was that Ian would not have the benefit of the 500 market if he was planning a non-compatible format and was considering the 500 format. So all he would get was tight faceplates and not enough room or ventilation for tubes.
To explain my "estimation" (some may say guess) that the 500 market is small, boutique and in the end fading (weak).
I think the reason DIY people like the 500 (including me) is that it reduces the amount of metalwork and power supply work you have to do.
The other reason I think is that there is a perceived market for 500 gear, and to be sure there is one, so other folks can build your stuff easily or buy it.
The reason that I think that market is weak is that I don't see many companies thriving in the marketplace. (There are a few small players, and some underfunded new players and players fading away, dropping out, etc.). If there was a substantial market, even a high end only market, then I would expect to see Avid buy or build a company in that space or Behringer making cheap knockoffs.
Also over the last few years I have watched the various announcements of so-and-so's new preamp, or module. I have kept track of comments like "we have sold over 100 of ..." (which was something I saw on a preamp that had been out for several years.) I know what the preamp sells for, I can guess what marketing costs, I can guess what the manufacturing and development costs, and I know what it costs to eat and keep a roof over your head in part of the world (a large part). And that company exists because they have some other sources of revenue or because they are a hobby or obsession (see below).
So based upon all of that, I am assuming that the market for 500 modules is a weak market. What I mean by that is that it would be unwise to invest money in developing a company in that market if your goal was to get a return.
That is not to say that a boutique company cannot survive in that market (API) or that a couple of small symbiotic competitors can't develop (purple, lindell, cartec) or that existing companies with boutique businesses can't feed modules into the market profitably (Neve, SSL). But kicking your way out of the heap of 500 series smallguys would be a lot of (expensive) work, and probably not financially worth it.
Some hobbies are just hobbies. When the get to be too big or too expensive or too time consuming to be called hobbies I guess they are "obsessions". If they get to the point where the investment is going in to make some sort of a return or living, well that would be a business.
I think a lot of these efforts are not financial... some appear to be hobbies, and some are clearly obsessions (and I think I see signs of at least a couple of "entrepreneurial rehab" cases ). I don't see many businesses developing.
But it is a lot of fun.