By NFC do you mean contactless cards or NFC payments via phone (eg: Apple Pay)? I'd suggest contactless cards would probably be the way forwards (it's similar tech anyway). I don't see the problem with paper tickets for Advances and International uses.
M-Tickets currently rely on QR codes, which are awkward and clunky (and have a terrible failure rate on the readers - often down to user incompetence, but still, that means they don't work and people get confused). I guess some sort of NFC "ticketing" might have technological advantages, but then you've got to switch on the NFC on your phone, which isn't great from a security standpoint (almost as secure as bluetooth).
Alternatively, you could definitely do smartcards better, you just need more bandwidth and more servers. The problem currently is that they work client-side, with lots of information on the card itself. A system where the card just holds a single globally unique identifier could have whatever back-end system it wants, with a web UI for people who are tech-savvy, and the ability for ticket-office staff to make changes otherwise.
Say, "normal operation", would have it operate on a direct-debit system to a bank account (like contactless cards), allowing unrestricted travel around whatever city-region you're in right now, then, you could go on-line and buy other tickets (for IC services), or set it to a "top-up" system (so you can control the money), or allow completely unrestricted travel (if you have the money), or even set it to "first-class" mode, add railcards etc etc etc.
You can do a lot, and get past people's irrational fears of using their cards to pay for stuff.