yup, i think it'll develop into a multi-layered market. i don't think privacy coins worth their salt will be listed on tightly regulated exchanges at all. i seriously doubt coinbase would ever list ZEC, just on the possibility they follow through and phase out transparent addresses entirely.
instead, we'll see a secondary market develop on decentralized exchanges. i think in some years, the vast majority of privacy coin volume will be on DEXs. as long as BTC can continue functioning as our reserve currency, that should work just fine.