If he is disclosing more detail of the potential plans so that it can be subject to opposition scrutiny and comment outside the public forum that seems pretty logical to me. After all, Sturgeon sees them as she is on COBRA, so it makes sense for the actual leader of the largest opposition party to be involved too, and once you do that, you do sort of have to invite the Lib Dems along as well in the aim to be fair. I'm assuming that the leader of Plaid is on COBRA as a devolved government leader, as is Arlene Foster for NI, but need to check that.