2) "It's cool to encourage more regular Solo players in imo because that shifts the odds of meeting a friendly" - no, it's not cool, as people choose Solo for a reason. You play how you want, so why not let them play how they want? Is anyone trying to "encourage" you to play differently? If so, how does that make you feel?
Not quite what I said. No judgements here, only more 'bodies' in any particular mode, by definition means more playstyles, means more depth of variety in that mode. The idea that Open should be (or even is) a PvP fest is both pretty inaccurate and defeats that variety. So do gankers ultimately.
3) "Easy and Hard would be more 'enticing' imo" - there is no easy mode. People play the mode that suits their mood or their skill level. Some people struggle with NPcs while others don't. It's personal, so your measuring stick only works for you.
50/50. You meet just as many NPC's in Open as you do in Solo. Players are harder to deal with though because they are an organic - as opposed to artifical - intelligence and as such are less predictable that any algorhythm. NPC's for example come with C&P wanted tags that flag what kind of behaviour you might expect. Players can pay off bounties, so you don't get that guarantee.
Reason I suggest tagging it Hard Mode (if you want to tag at all) as more enticing is because it presents itself as a challenge to test/improve skills. Calling it PvP Mode would sound more like a warning to anyone who's not sure.