Hello,
Has d20 3pp gone the way of the dodo? I've got my first 3pp supplement in the wings, but my partner and I suddenly find ourselves asking whether or not this is the right time to release. I know that WotC has been unkind to the 4e 3pp publishers and that Paizo has kept the 3pp tradition alive by playing host to a smattering of publishers of various quality... but is there a market, however small, for electronic or print 3pp supplements beyond questionable character option portfolios?
Anecdotal: my 3E products are still selling as sporadically as ever. However, I don't know how many pubs on the Forge are selling 3E material, and so you may not gather enough data to draw a decent conclusion. Have you asked the same question at RPG.net, or tried emailing 3E publishers at RPGNow about their general sales numbers since 4E came out?
Good luck!