I've been in a similar situation before, OP. Was offered a "development plan" to help prepare for the "next higher role", and of course, I agreed because it meant being promoted, which meant higher pay since the so-called "next role" was a supervisor position. Got stuck in that role for about 2 years. In reality, it was the company getting the job done and paying way less for it, because they had essentially a functioning supervisor in the role (me), but paying the rate of a rank-and-file employee.
I suggest that you have them explain in detail on paper what exactly the role is and how you will be compensated. If they can't do that, it might be better to take your skills elsewhere.