I'm not on the team making it, but if I had to make an educated guess based on amount of time to code and make assets, and make sound effects as well as alpha and beta test and assuming no lazy days off, it's probably about 1/3rd done by now.
And that's a generous estimate, if its as big as undertale yellow it might be less like around 1/8th.
These things take time and it could be anywhere from 1 to 999 years to finish.
I understand that you all are just curious, but stuff like this is distracting for devs.
Lets put it this way, "It might be abandoned but I doubt it."
Undertale yellow took 8 years to make it was indevlopment since 2016 and that had a team behind it, I would not be surprised if this took 20 years.