@hugo7 it looks like the wall surface is a couple of mm prouder than the wood frame. Can you not get some strips of pine/wood a couple of mm deep the same width as the frame, pin them to the wood frame, let your plasterers do their thing, then run a nice sharp blade between the plaster and the newly attached strips and then fill with a flexible caulk?
Should allow you to have a minimal level appearance and the caulk will hopefully avoid any cracking appearing.
I have used paintable exterior frame sealant/caulk in my place where wood meets plaster and the movement has been hidden by the flexible nature of the caulk.
This I think ^ is what I'd do if you didn't want to alter the skirting into the reveal.
The plaster bead thing fixed to the existing wood could be a bad idea as whilst the bead flange holes will let the plaster grab you cant be sure the wood wont move.
@hugo7 it looks like the wall surface is a couple of mm prouder than the wood frame. Can you not get some strips of pine/wood a couple of mm deep the same width as the frame, pin them to the wood frame, let your plasterers do their thing, then run a nice sharp blade between the plaster and the newly attached strips and then fill with a flexible caulk?
Should allow you to have a minimal level appearance and the caulk will hopefully avoid any cracking appearing.
I have used paintable exterior frame sealant/caulk in my place where wood meets plaster and the movement has been hidden by the flexible nature of the caulk.