Well, one of the proposals on this thread was to resist the mechanisation of agriculture and fishing. This amounts to preserving much of rural Wales as a museum of subsistence farming, which is terribly picturesque, but (without massive subsidy or a totally different set of industrial/agricultural policies across Europe since WW2), is going to leave the population grindingly poor.
Encouraging employers to hire locals would help, definitely. But for the more skilled / high-tech employers, that runs directly counter to the goal of not having big, bilingual universities. Even an aluminium plant can probably use skilled industrial chemists, and back in the day Bangor was quite good at those.
Taxing second homes and discouraging industries/developments which will require scads of incomers are all well and good (particularly the former), but what are you replacing them with as sources of employment? Having whatever devolved institutions exist located somewhere outside SE Wales would help, but the people of Cardiff and Swansea would be understandably irate - they'd be paying the freight.
Does better transport to England help preserve Welsh at all? Better transport (especially public transport) within North Wales would be lovely, but linking the whole better to e.g. Birmingham might be counterproductive.
Are you saying that everyone in Caernarfon and Llangefni is unemployed?