What sucks is that Ao is supposedly really, really, REALLY good and better than Sen, from what I know.
I mean, here's how I look at it.
The number one priority of both Falcom and XSEED has to be establishing and strengthening the franchise in the US, because if it can turn into a tentpole niche RPG franchise it makes it viable to keep profitably releasing future games.
Historically speaking, people who play a lot of JRPGs are very, very used to skipping games or playing things out of order, as long as it doesn't affect a directly-carried-over plotline. If (as several other mods have assured me) the connections from Zero/Ao to Sen are mostly in the setting and broader metaplot, it doesn't keep the game from being enjoyed as long as the gameplay and self-contained plotline are good.
Furthermore, since Sen 2 only came out in 2013 and Sen 3 (or the start of the next subseries) isn't out yet, it's entirely plausible for XSEED to nearly "catch up" and get in a position to bring over new entries within a year or so of their previous release. At that point platform issues start to be less significant and they can potentially keep up with future releases indefinitely.
If an ongoing fanbase for the series manages to get built up over here, who knows what happens down the line? Maybe XSEED fills a hole in their 2019 lineup with TITS TC; maybe Falcom brings out some new collected edition on a different system way down the line; maybe we just get the critical mass for a serious fan translation effort. Regardless, I think the best chances for the series in the long run are to focus on getting caught up with games in the present, rather than worrying about the games we've missed.