Thank you very much! I'm so glad that you are enjoying these. It really helps keep up my enthusiasm for continuing the project.
I am indeed working on other volumes (amid other projects)!
Volume Four will be Master Rank, featuring some very dangerous monsters that can hold their own against Elder Dragons, such as Ahtal-Ka, Espinas, and Brachydios. It will also have rules adapting the slinger/clutch claw (World/Iceborne), wirebugs and switch skills (Rise/Sunbreak), and Hunter Arts (Generations Ultimate) to the Monster Guts rules set.
After that, Volume Five will be the full roster of Elder Dragons from the mainline games (not including any variant forms, such as Risen Elder Dragons).
There may be some future volumes after that as well, depending on how much time and energy I can devote to the project.
I appreciate your patience as I work on these. I really love the MH franchise, and I want to make sure I get these monsters right in these supplements.