I know this is a rather open-ended topic, but unfortunately it's relevant to my situation. I'm 5', with 69.5 cm inseam, and based on a bike fitting I've been told that if I want a road bike that really fits me, I need to go with 650c wheels. I've recently acquired a 2010 Felt ZW100, in the petite size (with 650c wheels). My previous bike was a hybrid, and I plan on riding the Felt for a while to get a feel for the geometry. I'll fairly sure I'll eventually want to upgrade (the Felt is very entry-level), and based on my size it seems my only option is to get a custom bike.

My main concern is, what is the availability of 650c wheels in the future? Obviously no one can really answer this question, but I'm hoping someone with a feel for long term trends in the industry can chime in. It looks to me like 650c wheels on their way out, especially as bike manufacturers do not make production frames with 650c wheels anymore. If I end up getting a custom bike, I would like to keep it for many, many years; I'd be a bit upset, to put it lightly, if eventually I am no longer able to find wheels for my bike. It's already incredibly difficult to find 650c wheels wider than 23 mm (which is unfortunate, since I primarily use my bike to commute on the potholed roads of San Diego).

As a follow-up question, are there other small wheel sizes to consider, and how difficult is it to build a bike that can take more than one size wheel? What sort of design considerations would need to take place? Essentially, given the fickleness of industry standards, how can I best hedge my bets when ordering a custom bike so that I have the greatest likelihood of finding wheels for my bike in the future? R+E Cycles, for example, has built road bikes that can take both 650c and 26" wheels, although this means that the brakes require special consideration.