In terms of modular design, the idea was to keep each segment of the game as independent as possible. If we could carry over only the absolute core of things - stats, hit points, AC - then it would be much easy to add new rules elements or adjust things. The DMG had a ton of variant rules because of that thinking.Thank you for response! Any chance you can give us more insight on what the original design team thought about "modular" design and how it was implemented in 5e? You may or may not be aware, but that is an often debated subject on these boards.
Also, I've been following your Odyssey work and it is really interesting. Thank you for digging into the nuts and bolts of 5e an looking at ways to make it better. I've been waiting to update my homebrew 5e game because I like a lot of what you have been developing (not 100%, but a lot). Any goals / plans for when you might publish the system?
I think that modular shifts a bit depending on what an individual person think it means. It probably would have been smarter back in the day to say things like "flexible" or "easy to adapt". Like compatible, it's a term that invites people to fill it in with their own take on what it means.
It's funny that the biggest pain point in the game - monsters - has the most instances of drawing too much from the rest of the system. For instance, monsters were not supposed to use proficiency based on their CR. They were instead supposed to have a skill rating that could change based on their story and nature.
Odyssey and the work on my Patreon is definitely going to see publication in some format. I've been having some great chats with publishers, but too early to say where things might settle.