Good day,
new firmwares releases will not be fully supported by old hardware. You must consider if you want follow new features or not. Now the new F7 has replaced the F4, and with new hardware you can find also new generation of sensor and others improvements.
Pixhawk1 familly controller still have some time before beeing discontinue, I would say still 2 years to go before we get issues integrating new features.
@Dave84 F7 will not replace F4 … that are differents proc, and on ardupilot we will probably skip a large part of F7 to directly jump to H7 serie that are even more powerfull.