This is a fascinating issue, though it looks like from that article that there is no consensus. I think I’d side on it being kosher and pareve though as Rabbi Lau asserts in that article. The root principle of kosher laws is food safety and kindness to animals (however misguided that is given the we now know schechting an animal is actually horrifically cruel to it). Moreover, the rule against mixing meat and dairy derives from the prohibition on boiling a calf in its mother’s milk. Cultivated meat is the least cruel method of acquiring meat obviously and it has no mother, so kosher and pareve in my book.
The tax you pay is one the net gain, which is the amount realized less the base of the good (i.e., what you paid to acquire). I’m not a tax expert, and real estate can get really fucky with this stuff, but that’s my understanding of the fundamental rules for taxation.