I'm not entirely sure on what the exact solution is for Vlachia, but iirc, one of the current problems with Vlachia from
The House of Iron: Chips and Cheese is that Vlachs were emigrating to Romania in huge numbers, which cuts into the landowner elite that feeds the majority of Constantinople through their grain exports. Not to mention these large landowners themselves were buying up land from the lower classes, leaving them landless and poor, forcing them to migrate to Romania in the first place. Additionally, Roman imports of manufactured goods without any tariffs basically put many Vlach artisans out of a job since anything out of Romania will vastly exceed Vlach products in quality and price. On top of the low population figures, a poor economy, and low social mobility (probably nonexistent because of serfdom), Vlachia in the 1630s/1640s sounds like a pretty terrible place to live.
The Vlachian King or the Diet would have to solve the majority of these problems if Vlachia is going to prosper again as a state comparable to the Despotate of Sicily or Egypt in development, which is difficult when trying to enact land reform or tariffs is something that is against Roman interests in the first place (or at least the landowning elites of the Diet).
Seems like political revolution is inevitable given the extreme disparity between the peasantry/serfs and the landowners and just the overall poverty of the country (further compounded with the Little Ice Age and the Roman depression).
Trying to implement an Agricultural Revolution through new technology or new foodstuffs would be exceptionally difficult in a place where landowning elites are reliant on serfs and people aren't used to complicated machinery or crops like maize, potatoes, amaranth, and etc. (Assuming Terranovan crops even made it to Vlachia in the first place).
Plus anything that Vlachia does in terms of agricultural development, Sicily, Romania, Scythia, and Egypt can do it far better than them, further compounding such issues.
Vlachia can't do this kind of reform alone, they'd need a large amount of Roman cooperation (Subsidies and expertise from Roman farmers/scientists), and I don't know if Constantinople is willing to put in the money unless they're pushed towards that kind of settlement.