You'd need the stadia as well, in order for it to work.
I would say
Tier 1 Llanelli, Swansea, RGC 1404, Bridgend, Cardiff, Pontypridd, Merthyr, Newport (Super 8, U23s)
Tier 2 Ebbw Vale, Aberavon, Carmarthen Quins, Neath, Bargoed, Caerphilly, Cross Keys, Bedwas (emphasis on developing U18s)
For Scotland:
Glasgow & Edinburgh plus
Borders (revive old team)
Ayrshire (could ground-share at Kilmarnock FC)
Central Belt Team (could ground-share at St. Johnstone FC)
Highlands (could ground-share at Inverness Caledonian Thistle FC or Ross County FC). The former would be my choice as they will need extra funding if they do not return to the SPL in the next few years. A ground-share could save them and help the development of rugby north of Inverness as well.