Tiagra 4700 has been out a very long time. I haven't heard many complaints that aren't just the same adjustment or installation issues that 105, Ultegra and DuraAce will have.

My son had Tiagra 4700 on his bike for awhile. Only replaced it because I had a 105 5800 that was sitting unused as I decided not to upgrade one of my other bikes.

As for parts later on, probably not an issue. 10 speed bikes will be offered new for a long time. Shimano will probably maintain something that is compatible even if they make Tiagra 11 speed and push 10 speed further down the list.