Some thoughts on pros and cons of an original system design in the TTRPG space:
Pros:
- Bespoke, so it can potentially more closely accomplish exactly what your aim is.
- Perhaps the only way to accomplish something people don't normally attempt.
- Don't have to master some other system before creating for it.
- May involve aspects of creativity and design that you find personally appealing.
- Don't have to read/understand SRD licences.
- To the extent that it's perceived as being holistically "more creative" it maybe boosts your interactions with curators of indie game fests, or contest judges.
- Slightly more likely to appeal to your peers in the indie creator community? ¯\_(ツ)_/¯
Cons
- Creating something new out the whole cloth is hard.
- Creating something new at a high quality with depth of complexity is very hard.
- Holding complexity of the end product constant, you'll still really need to add lots more playtesting.
- More effort for writing and editing.
- No built in audience who already love the system but want more stuff to do.
- A fair number of people who attempt this seem to have played very few games, and seem constrained by the paradigms of ones they have--risk of doing the extra work without achieving the benefits of bespoke originality.