I’ve always wanted to try the X-Force equipment, but I don’t think it will ever happen. I guess they are just too expensive for most gyms.
One development does look interesting though. The Tonal strength training machine, which uses programmable electromagnetic resistance, allows the user to dial in a pre determined amount of negative upload.
So if you set up the machine to do chest presses with 100 lbs of resistance, you can enable a negative upload feature that will increase the resistance only on the eccentric. Dial in 20% and you will get 100 lbs on the concentric and 120 lbs on the eccentric. Basically, it seems to do what the Xforce machines do, only via programmable electromagnetic resistance, rather than tilting weight stacks. They also have programs which simulate the use of chains, i.e., accomodating resistance.