A Pathfinder equivalent of D20 Modern has been brought up more than once on these boards, and, inspired by some pictures like
this,
this,
this,
this, and
this, I've done some thinking on what I think would make a good modernized game based off of the Pathfinder system.
If you viewed the pictures I linked to, you have no doubt noticed what they all have in common: an example of magic or a fantasy trope in a modern environment. This brings us to my first thought on a modern Pathfinder: the fact that I think it needs to be a fantasy game. A big part of Pathfinder is the fantasy elements, and I've grown quite fond of them. I want to keep those elements for this project. Personally, I rather like the idea of elves in jeans and t-shirts and wizards keeping their spellbooks on touch screen tablets.
On to the class system, one of the biggest parts of how D20 works. I like the D20 Modern Advanced Class system, but not the basic class system. Rather than have basic classes for each stat, I'd like to go with Warrior, Expert, and Mage. Furthermore, I'd like to have a variety of archetypes for the advanced classes, allowing a large array of customization without having a whole mess of classes.
As for D20 Modern's background system, I'm looking towards a hybridization with the Pathfinder trait system. I'm looking towards making backgrounds a trait category and having players select one trait from each category at character creation. I want to tie class skills to this system rather than classes, so that how you grew up effects what skills you've developed. Each trait would have five associated skills, and you'd pick three from each trait you have.
Combat needs to encourage movement more, perhaps by making Shot on the Run something built into the system. The cover system should encourage players to use it, while allowing for cover to be destroyed or penetrated. Fixed DC reflex saves for explosions and automatic weapons are simply a no-go. They don't keep up with level changes. I'm not sure what to do instead yet, but something different needs to be done.
The biggest thing, however, is that it needs to have it's own campaign setting while being easily modable to a homebrew effort, just like Pathfinder is. You need to be able to pick this up and play it without having to spend forever building your own setting first.
This wasn't a very long OP, as there aren't a giant number of steps necessary here. They are, however, some rather big steps. Still, I think a Pathfinder D20 Modern can be an excellent game rather than aspiring to D20 Modern's mediocrity.
More thoughts, regarding to specific campaign setting details, later.