Can I still subscribe to Farcaster Pro?

Yes. Farcaster Pro is bound to your account (FID) and will give you additional features for your account over time.

Again, the first 10,000 subscriptions included a limited edition NFT. 
But all future features we're working on will go to all Pro subscribers. It won't matter if you have the NFT or not.

It's optional, does not increase your reach, visibility or rewards.

There will also be plenty of features we add for all accounts! It will be a mix.

Is this why I can't cast my "thank you" video?

Or is that a separate issue?

buying it now after the first 10000 is just burning money