People are conducting transactions using Bitcoin, and complaints about transaction times only arise in a tiny minority of instances, therefore transaction time is not a problem.
Actually I've noticed more and more threads lately about confirmation time stretching over an hour, I think due to Bitcoin growing in general, hence more transactions. Aside from that if you poll the community on whether they would rather have instantly trustworthy transfers or deal with confirmations I'd be willing to put bitcoins on what the result would be.
In addition to this, Bitcoin confirmation is faster than any other means of online transaction, when you compare like to like.
Please be practical. We're not out to dissect bitcoin and financial services. We're simply asking what people would likely prefer to do in the future.
An "instant" PayPal transfer is reversible for at least several months, and probably indefinitely.
The thing about reversibility is not important for the majority of transactions, which are largely legal. If you pay a dentist, or for a cup of coffee are you really thinking reversibility will be an issue? Also, a company can offer a no-reverse transaction option.
Bitcoin transaction also show up within a matter of seconds and are typically irreversible within an hour.
A Bitcoin transaction merely showing up is not considered by the community (for good reason) to be a good indicator a transaction is valid. I've addressed reversibility above.
Assuming equivalent UIs, what theoretical advantages to your third party off-chain service provide have that zero confirmation Bitcoin transactions don't already provide?
Assurance the transaction is valid.
Although I've got other things to do I'm happy to continue addressing your concerns to try and convince you, because I think I'm right. However, if you are unwilling to be convinced please let me know so we can save both of us and this thread some time.