If I understand correct from Athom it should be possible for you to upgrade the App to SDK3 with your current Homey (Pro) (Early 2019) or older.
( But you are right, for some things it could be better to test also with a new device, just to be sure it works if users mention issue.)
But apart from that, I understand you now open the “Donations” to port [App][Pro] HomeyKit
I just realized the same for myself,
if only 50% of my users of my App donated 1€ it would compensate my extra investment that gave some “relational discussions” and even give me half of the const to take here out for a dinner.
But I was that “naïve” I sponsored Athom to get a 
Tag on my name.
Losing my links to Paypal and Patreon on my apps…
