Okay, I've been working all day and I come home to this, so I guess I should shoot in my own interpretation.
First of all, keep in mind that the MGE (Monster Girl Encyclopedia) is a child of the original thing that set monster girls on the chart, namely Monster Girl Quest, or Monmuso Quest if you prefer the Japanese title. It's a visual novel, but more prominently, it's an H-story. The game is literally about fucking every girl you meet. I gave the game a try, and the gameplay style promotes dying in the battles so you can see the sex scenes.
I don't think going for such an approach would be the wisest of approaches. Namely because it would heavily limit variety. As mentioned above, there are many alternatives that some can consume, which I think is a better baseline. Having cum as a supplement is one thing, but it would kind of ruin some of the originality with the races that rely on cum as their source of nutrition, say succubi (Well, to be fair it's said to be sexual tension but anyways) or lamia which I believe is listed in the encyclopedia as a heavy cum-consumer compared to a lot of the other races, whom can rely on other things as well.