Well, yes, you could use one 202 instead of two 200s or 100s, since the 202 has two line ports (RJ-11). This would be if you want to use the two services independently on two different phone wire pairs to different telephones (or a multi-line phone).
But, if you're going to get rid of Future 9, I wouldn't bother. Don't forget, the 200 still has 4 service provider slots, and you can certainly configure it to have Google Voice on SP1 and Future 9 or some other SIP provider on SP2.
The common scenario is: GV on SP1, SIP ITSP on SP2. Use GV by default for (free) outbound calling, since it's on SP1. Remove the check mark for Google Chat on your GV settings page, so it won't be used for inbound, and add and enable the SIP ITSP number on that GV Phones page, so it becomes your inbound forwarding destination. Depending on the SIP ITSP, this gives you Caller ID Name (CNAM) support.