I think Toady could make more money by placing advertisement in DF. Just some common brands, maybe some satirical life-style tied to soft drinks or reliable automobiles. This could possibly make development bigger and faster. Toady would get more money and he could buy a lot of luxurious healthcare and computer equipment enabling him to realizing his vision even faster.
Seriously, this was in a PM from somebody who had a low income and had played DF for three years, even on hardware that could easily play modern games up until this date.
To respond simply, it is unlikely that product placement would be a viable means of funding. Not only is there the very significant customer alienation factor that must be taken into account were any such policy to be implemented, there is also the fact that DF is fundamentally a rather niche game. The target audience that would be reached is quite low, comparatively speaking, and therefore, the desire for advertising in DF on the part of most business would be quite low. The ability to implement it effectively is also questionable; parody, as you suggest, is quite different from product placement, and direct product placement would be quite immersion-breaking. In other words, it'd drive off players and bring in very little money.
Besides, there are plenty of more effective means of profit generation, should such be desired. As far as I am aware, given the significant donation income, there has been little need on the part of the developers to expand the revenue stream further.