Trading a continual long term revenue source for a single one off payment, probably isn't very compelling.
The risk being that a slow development pace will allow Atom to eat ST's lunch. Then any future revenue falls off a cliff.
Use Kickstarter to open source it and you both cash in and do the community a favour.
Last I tried Atom it's quite a long way from offering any significant advantage over ST and has it's own risks due to not having a clear revenue model. If the ST devs believe that they can sell 100K licenses over say 5-10 years at $60 each then that sets the kickstarter goal in the region of $6M without offering any rewards for backers which seems like a pretty unrealistic target.