IMHO most Eth L2s already show more promise than PayPal as a future payment rail tech, despite them all basically being in beta state. Much lower fees, faster transactions, permissionless withdrawals, fully programmable, negligible energy usage now thanks to PoS.
All being said and done, all the L2 are just centralization projects. These chains and tokens will always be controlled by a small number of early movers. Eventually, it doesn't even fulfill the very purpose of all these tokens - being peer to peer money.
(IMHO it’s likely that other tech/protocols will emerge in 3-5 yrs that supersedes the protocols in development today.)
Lots of typical crypto caveats - eg: USDC on an L2 is centralized around Circle’s ability to redeem. Protocols can have bugs that make coins go poof. Non custodial ownership is harder for many users than asking PayPal or a bank not to lose their funds. L2s specifically are typically run by a single sequencer who could potentially disrupt your ability to use the network smoothly (but then you could use an escape hatch to permissionlessly get your funds out if that happens).
The UI is really up to the apps, the good thing is there are many teams working on payments so there will be plenty to choose from to find the UI you like, and people will be able to pay via the same wallet. Stripe already has USDC payments on crypto rails and Visa is working with Starknet to integrate with these L2s too.
All the L2s with their usage, security, speed and tradeoffs are at http://l2beat.com