the moment I (and i dare say a vast majority of bleach fandom) have been waiting for has happened!!!! the last picture of this chapter was every fanboy dream i've been having for the last 200 or so chapters since we last saw Isshin in anything other than an omake chapter!! what possiblities!! will this be a triumphant father son victory over the big bad?? we will get to see what Isshins shikai and possibly Bankai are maybe, just maybe Isshin will teach Ichigo to something other than a getsuga!!!!!!!!!
makes me wonder though, considering the other shinigami refer to him and Kurosaki-kun why hasn't anyone mentioned his dad before? i know this has been discussed at length before but really if Aizen knew of him then how the hell does he fit into the structure of the Gotei 13? i know he didn't officially say he was a captain before, he just talked about Captain level reiatsu, but i figure as of know we can officially assume he is of Captain or higher level rank now. so my thoughts are maybe he was the captain of squad 3 prior of the TBtP arc and was succeeded in that post by Rose. but much like Hikifune was upgraded into the royal guard. this still doesn't explain why someone like Shunsui, Jushiro or Unohana have never mentioned him being the son of Isshin, to each other or anyone else, but judging by the fact that Uruhara knows him, treats him as a superior and hasn't said anything to anyone i guess his status as possible Squad Zero is likely.
Also Kubo seems to be very fond of showing off differences in power between various levels of the groups he created. I mentioned before that if Squad Zero were to get involved that it would probably be a single member with incredible power unlike anything we've seen to date. Also the only point they would get involved would be if Yama-jii was put out of commision which is obviously the case now (even if he is not actually dead).
so in conclusion think that Isshin was a G13 captain, got promoted along whatever lines Hikifune did which is why none of the current captains ever acknowledge the link even to each other. and his power level will be of the chart compared to what we've seen so far.