Hello @jbrains ! Glad to have you here. I’m new to Discourse admin. Some related links for folks who may not have seen them: yesterday I updated the pinned
Welcome to the Plain Text Accounting forum!. It says
to help move our community discussions to a community-owned place with a stable future and a more pleasant and modern user experience.
(a wordier earlier draft said “move the center of”). And that links to
A trial of Discourse for Plain Text Accounting discussions
which gives more background and motivation.
To answer more directly, it’s up to the community where it would like to discuss things; I personally am ready for something new and want to give Discourse a try in particular. I feel it has a pretty good chance of getting traction and actually growing the community in a new way. But it’s easy to have big visions, and it might not happen. 
As long as Reddit keeps working I know probably a lot of people will stay there. But if it doesn’t, this will be here. I’ve also set up mirroring of the reddit’s RSS feed here, which if it works may help reduce fragmentation a little.
Which google group do you mean ? The PTA apps have their own google-based mailing lists, but there’s no general PTA one AFAIK.