Usually I might say that from the attitude of scripting this rule again in 2014(?), it’s fairly cheap.
However while you’ve really performed the sport for a when you understand which you can’t examine the four CR or ranges distinction between a degree 6 druid and the CR 2 kinds she will assume on one hand, and the whopping 10 CR/ranges distinction between a degree 15 druid and her CR 5 kinds.
What is sort of cheap at low ranges simply turns into irrelevant at excessive. (The PHB writers do acknowledge this by permitting degree 10 druids entry to CR 5 elementals. At that actual spot, you acquire entry to “half your degree” kinds, even when it does not scale as you degree up)
So my first thought was: what about altering the method for high-level druids? That’s, add the next line to the “Circle Types” function, PHB web page 69:
Beginning at 12th degree, you possibly can remodel right into a beast
with a problem score as excessive as your druid degree
divided by 2, rounded down.
The following step was to understand that, by RAW, that may quantity to little or no, since there merely aren’t many excessive CR beasts.
Which brings us to this thread!
If we maintain refraining from discussing Dragons, I might say Monstrosities (or, particularly, the Monstrous Beast sort that used to exist) could be the apparent subsequent sort to open up, after Beasts and Elementals.
So. If my preliminary query, “are you conscious of any current fan doc that does the work for me?” will get a adverse reply, my subsequent line of strategy is:
Would you say a restrict on Intelligence is an easy and stylish, but practical, technique of filtering away these Monstrosities that may not be suitably “beastly” for a Moon Druid?