If you have an older home with antique lamps & custom wood/cabinets built around incan fixtures, it is naive to assume all the new LED/flurescent bulbs will work. I assure you they won't. In addition, I have not yet seen an LED that I like using over the color and other features of an incan.
And you don't think these problems will be solved in four years time? Four years is an eternity in the LED industry. Think what we had four years ago and what we have now. I think in 2003 state of the art for a Luxeon was about 20 lm/W, and many came with an awful green tint. Now LEDs are mostly pure white, with neither a blue nor a yellow tint, and 4 to 5 times as efficient. We'll solve any remaining color issues (mostly color rendering of deep reds) by then I'm sure. And by definition LEDs are small. As their efficiency creeps up, it should be possible to make screw-in replacements not much larger than the socket.
Also, you're the exception, not the rule. Few people have thousands of dollars of custom woodwork built around incandescent sockets. Most people just have a junction box in the ceiling which can accomodate any type of fixture. Most people have crappy fixtures which need to be replaced every few years anyway.
I can think of one reason to stock on bulbs, though. There will likely be people who refuse to switch to anything else, indeed won't even look at anything else because in their mind "incandescent is better". I suppose these are the same type of people who thought candles were better when incandescent first came out. Those are the people I'll be able to sell my stock of light bulbs to for $50 a piece around 2020.
While we probably won't ban
use of incandescent, for now anyway, I can easily think of ways to discourage their use. The power company can occasionally send a few voltage spikes lasting several seconds down the line. Most modern equipement will cope just fine. Indeed, a lot of equipement these days can run off anywhere from 85 to 265 VAC. The incandescent bulbs however would be zapped instantly by a 260V surge. Don't laugh. If I were running a power company and were faced with the highly unpopular choice of building a new power plant, or getting people to cut back on their usage, I might well do exactly such a thing. IIRC there are also other types of voltage signatures which would zap incandescents without affecting anything else.
BTW, my guess is LED technology will progress so fast that in four or five years time there won't be any incandescents on store shelves, ban or not. We're already there efficiency-wise. Color is not perfect, but acceptable for general lighting (indeed much nicer than incandescents and most fluorescents). Cost is still a factor, but $0.20, 1000 lumen emitters in 5 years will be entirely possible given Moore's law. Under those circumstances, it's really hard to see anybody continuing to mass produce incandescents.
