They'll sell the most lucrative products first while ramping up the R&D to tap into more markets when those eventually saturate. So, 30kwh battery car doesn't make any sense for tesla because they'd eat into the sales of cars that make much more profit per unit. The model 3 has shown that they are really good at upselling software features and extra kwh (read even higher profit margins).

Their strategy seems pretty clear to me as they have plenty of products in a late stage of R&D that they could sell many off if only they had the production capacity to meet demand. They are basically tackling this in order of profitability. Model Y is next. They have the Tesla semi ready to go as well in limited volumes and they've been talking about a new roadster and model s as well. That should keep them absorbing whatever amount of kwh they can squeeze out of their factories for years to come.

So, I don't see what value a low capacity cheap car would add. They'd need to sell many more of those than of their other products to make the same amount of profit and they are basically bottle necked on production capacity already. It doesn't make sense for them to even consider sacrificing factory space for this until after they build a lot more production capacity and the market for higher end options is saturated (which will take quite a few years).