Off the top of my head, you might run into a problem with the little known Common Law concept of the right of ownership...
More seriously, the strength of the agricultural lobby in Europe is more to do with its contribution to output, employment and the social fabric of France and Germany, than it has to with Irish (or Greek, or Portuguese) farmers.
- Should CAP reform have moved at a faster pace? Almost certainly.
- Did CAP establish an over reliance on production subsidies and take farmers' eye off the real game (ie, demand-led production and innovation)? Unfortunately yes.
You are conflating productivity and salaries -- one of the key reasons we're in the current mess. Had productivity been increasing (at least) as fast as our collective payroll, then we'd still be a competitive economy. Perversely, the opposite of your argument is more accurate. Had wages and demand for plasterboard cubicles (houses) not soared to the unsustainable levels we now know they did, neither would land prices have became so grossly inflated.
Agricultural reforms are progressing -- with all the maneuverability of the Titanic. The decoupling of subsidies from (over)production has long since been implemented, as have programmes of farm retirement and modernisation. In the very near future, it's highly likely that what remains of farming will be entirely market-driven and the single farm payment will be "modulated" out of existence.
Nationalising sheds and grassland is neither here nor there.