Started thinking about this question, one I think the IRS is pondering as well.   Trades between coins are to be considered taxable, no more pushing the tax burden down the road with trades until you cash out.  Not sure of the best way to record these. Online software I have seen is expensive. CoinTracking.info and CryptoCompare.com seem to be highly rated. If you only make a few trades a spreadsheet. Using a trading bot and hundreds of trades, painful.

Sorry drifted away there. Back to your question, not sure how you would want someone to share their cost basis? I wouldn't want to on an open forum, plus who is to say if it is all made up?  Would almost need a bonded third party to verify account ownership and cost information. Not really worth it for a message board discussion. Maybe an idea for a blockchain solution? I mean if it can work for Kitties....