I very much don't like this idea and this is for a few reasons:
1. We do not know what the devs still have in store for us with the.. uh store. There may be other things to buy than dwarfs an dragons that could make you want to spent some serious crowns. Keep in mind there is also some promise of navy and naval combat on the horizon, if I remember right.
2. People paid for that, as soon as the micro payment is active again, there will be people who spent money for their crowns, partly because they have no time to get them otherwise, it would suck for them to lose them this way.
3. You would make this game unenjoyable for everyone who is not good at PvP and does not keep up with the cookiecutter tactics (implying there is one right then), as you have no real choice to avoid PvP, especially once city combat is activated you would scare of a lot of casual gamers, and people who suck at PvP. (Coincidentally I do that
So yeah, give us more ways to spent our crowns - but absolutley "no" to punishing sub par players