Two ways I look at this:
1) I'd love an affordable way to process 5x7 because the price of Jobo Expert Drums is out of control
2) Processing just two sheets of film at a time is a deal breaker for me. Way too much time investment for way too little finished film
While I am sure you'd like to keep the whole system in-house, have you considered piggybacking off the work of Jobo and creating a 5x7-sized reel to fit their 2500-system tanks? Basically, it'd be like a 2509n reel on steroids. The tanks are affordable, can be processed with or without a Jobo machine, and many people already have them for 35mm/120/4x5. I would HAPPILY pay you $60 per reel if it'd hold 4 or more (preferably 6!) sheets of 5x7 per reel to fit tanks I already own.