It's a great idea, but find a way without a hardfork.

Graphene based cryptos are far more capable of implementing hardfork/mandatory changes than BTC is, we already have several other hardfork worthy changes in BTS' roadmap, we could throw in the change during one of these upgrade periods.

Take Steem for example, they've performed 19 HFs successfully thus far!

would be cool if there was a wizard bot setup, like byteball, that let's you setup an account and you can link btc addresses via signed message.
this would be more centralized, however, Assets need more functions anyways. such as "lock max amount".

This would be centralized though with a counterparty/middleman risk & we would need to monitor signed transactions on one or many Bitcoin split blockchains for a long period of time (unless there was a limited period of time to claim the tokens?).