So you are saying P3DV4.3 and below version are no longer supported, is that correct?
Exactly.
Not really news, since several other developers (most notably, PMDG) already announced the minimum P3D version they'll support with upcoming updates, will be 4.4.
I think supporting up top the second last version, is more than reasonable, since 4.4 was released in November last year, so, if the reason for not updating to it was some other 3rd party software that wasn't updated yet to support it, after 9 months if there's still something not outdated for 4.4, maybe it might be time to question if it's worth still using it in the first place.
The update to 4.5 is free, so I don't really see any reasons for not updating.