Beside IBIS, A7 II also has faster autofocus and tracking, and XAVC S codec with S Log2 profile. This announcement was a total surprise. Hopefully the A7S II with 4k internal recording will be next.
E10-18mm OSS, FE16-35mm OSS Zeiss, and FE90mm OSS Macro G should be good for full frame uw use.
Yes, the E10-18mm will work perfectly on an A7, using the 12-17mm range since the image circle will cover the entire FF sensor - no need to use the crop mode. Here are 10-18mm/A7r examples. 12mm is considerably wider than 16mm.