FIT is unrelated, you keep your export meter & report it to your FIT provider as normal.
Actually, I think (based on my recent research) that this is not correct.
I am a very technical, clued up engineer and did my own solar PV and self-use system several years ago.
Eon (my fit supplier) just told me categorically that my FIT payments would not change based on having a SMETS2 meter. Only a FIT Export meter would require them to use those actual export readings rather than 50% deemed export and that a SMETS2 meter is NOT such a device.
However, the EDF application for a current smart meter includes a statement that FIT Export will change to an actual basis. On investigation, a very knowledgeable specialist with EDF's green team explained that OFGEM have already advised that where a device exists that provides actual export values, this will be used rather than the 50% deemed value. This is not the case as of today, but in the next 6 - 12 months it is expected that the change will be implemented.
I expect that the trick is that as of today, a smart meter is not listed as a suitable export measurement device, so is not used for providing that info, but in due course that definition can (and most likely will) be changed.
In my case, that could cost me £150 pa.
The other point made was that in dues course it will be decided that the existing standard / E7 meters are end-of-life and must be replaced. So eventually PV owners with self-use systems (zappi, power wall, EV day charging, Immersun / diverter immersion heater etc) who have high self use and lower actual export will be worse off.