For the amount of time and trouble we need to grow monster essence, I'd like to see the ability to actually craft a spawn egg for the mob.

The point is to be able to grow the mob drops, not the mobs themselves. Don't think I will be adding this.

If you want those recipes you can use CraftTweaker to add them.

Newly updated: CraftTweaker script for spawn eggs. (May 8 2017)

Currently defaults to requiring mob chunks, but there are tables and code for three variations included: mob chunks plus tier essence, the (default) mob chunks only, or just essence.

Now updated with recipes for chunkless mobs, though many of those are commented out by default.