It seems we are again challenging our ideas of sidechains.

I am not so much interested in sidechains supported by native currencies. They are essentially altcoins and I have historically stayed away from these.

If 1:1 pegs can achieve stable transfer of BTCs between chains then this is where, to me, the innovation is. In that case, price of the unit ideally gravitates toward parity with original BTC for reasons discussed before in this thread. It is possible the BTC unit resting on a sidechain would have a slightly discounted market price for security concerns but I expect that gap to significantly narrow once/if technology matures.