I'd like to see the datalogs on that. A track prepped (caged, slicks, etc.) STi will see 1.7+ and a bit more with decent aero and speeds. I'd be very impressed if these cars come close to ~2g lateral. Hopefully these values are true, and not being measured with a cell phone app. It's been years since I calculated the critical lateral force, but I want to say it is ~1.82Gs, theoretically. Regardless, if anyone has a true 2G capable car I would like to see how our product performs at these levels on track. Like I said, to date no one has been abe to starve our setup. Not to pat ourselves on the back too much, but we have even replaced other aftermarket setups that have shown pressure problems under track condition. of course every track is different and while I have seen LOTS in this industry, I've not seen it all. So I'm open to exploring limits and coming up with solutions.
So to answer your question... for a wet sump solution our setup is the best performing for an EJ engine, that is currently available. Having not seen oiling issues to date, I'd say it's a good option. Although, you are talking about forces that are beyond what our high end hard core track guys are seeing. Further testing should be done to prove or dispove the capabilities to the levels you are discussing.
Sadly, I'm not all that familiar with the 818 engine mounting design, but droping 2-3" in an Impreza chassis means a redesigned engine cradle or replacing engine mounts with an adapter plate. Even at that, it would be very difficult to swap out mounts only and get a drop that significant. Most aftermarket drop mounts, drop ~6-12mm. I would recommend replacing the OEM pan with a dry-sump pan as it saves a lot of work and is already designed to work correctly. Desiging and plumbing a dry sump system is daunting task if you've never done it before. I recommend searching dry-sump diagrams to get an idea of the parts/pieces needed. Here is a simple diagram of a 4-stage...
1381_dry_sump_oil_systemoil_system_schematic_1.jpg
If testing did prove our wet sump was problematic at super high loads... I do have a multi-pickup design I backburnered years ago that would not cost as much as a dry sump, but still pull oil from the heads as well as the sump. I stopped development because... it never became necessary. Hmmmm