We've been discussing this idea here: https://github.com/bitshares/bsips/issues/28#issuecomment-324512215

I think it could be successful in preventing exchanges from locking away hot wallet funds, however we've seen exchanges not move their cold wallet funds for 10 months solid in the past - such cold wallets may be locked away for an even greater share of voting power (if non-exchange users don't lock away their funds).

I think that such a proposal may cause smartcoin liquidity issues though an ultimate goal of successful smartcoin utilization is that less BTS are liquid. So it may be great for our mcap and voting system as long as users can perhaps receive smartcoins as an accelerated exit and if exchanges don't lock away cold storage funds.

Overall I like the idea more so than blacklisting accounts.