The thing is, usually, mechs from games don't make it into SRW. Of course, Virtual On MARZ is the sole exception, probably due to the single-player campaign and whatnot. The chances of Square Enix asking to put in any of the mechs into SRW is slim to none, despite Xenogears' popularity. Xenosaga has a better shot, since Bandai is the parent company of Banpresto and since Namco is part of the company, they might throw in some Xenosaga mechs, not that I'm counting on it.
In any case, most of the recent series don't have a shot at being in SRW because it usually takes a year or two. Hell, it took Seed Destiny 4 years to get into SRW.