Good clients change, bad clients get left behind.  There might be a graceful way to do it that doesnt require everyone to upgrade.  

For profile you can keep the same profile pic, maybe have a little dot on there to indicate subkey.  It can be verified.  Perhaps also something can go in NIP-05.

Tricky thing is pulling in all the replies etc.  Worst case is that someone follows your subkey too.  Then the WoT stuff gets more complex.  Also NIP-98 gets more complext.  It could be done in stages.

I do admit I'm probably over-simplifying things!