Will tzt3 later be able to handle 455 kHz?
If connecting tztxl with sidescan 455 kHz on network with tzt2bb will it share sidescan function?
Or tzt3.
Will sidescan function be accessible with timezero pro?
No, it requires needed hardware and the development period for TZT3 is long over.
I don't know what TimeZero would show as that isn't something we deal with. TZ/Nobeltec support can tell you and what modules might need to be purchased etc. For the XL and TZT3, yes they can see the internal sounder of the other series including side-scan. So as your example the TZTXL 455 side-scan can be view on a properly mixed TZT3 on the same network.