I am sure you are probably already aware that you can buy aftermarket receivers for your garage door opener (for example, from Chamberlain/Liftmaster or Genie) that simply close two contacts for one second when they get the garage door signal. These are 100% HomeLink compatible, and both of those brands support “rolling codes” to prevent signal copying. Those contacts could go straight to a EzIO2x4 or similar.
I am not sure what you plan to let your X10-driven HomeLink do, but hopefully it isn’t to open doors. I would hate to think that any moron with an X10 keypad could get into my house.
That brought up another thought – X10 sells a wireless alarm system with sensors that use the same frequency as their other devices. Anyone with an X10 RF keypad can just hold down any key to jam the frequency which merrily prevents any nearby X10 alarm system from working at all. I also have observed an X10 alarm system act as though it received some RF command when really I had just made a static spark with my finger and the X10 system interpreted the resulting RF noise as a command. Bottom line, X10 RF is a crappy choice for anything that HAS to work.