Halfway to Manhattan
I was going to suggest the Blue Bottle, which is a BYOB. It's a bit off the beaten path in Hopewell. The food is wonderful, and you won't be disappointed. I haven't tried Eno Terra, but it has gotten very good reviews on CH. You might do well to post this on the Mid-atlantic board, as there are many active NJ posters. The moderators will likely shut this topic down, once you mention NJ on the PA board.
Most of the spots at the halfway point would be in NJ.
We actually were in the same situation a few weeks ago, my husband had a colleague in Newark and we wanted to meet halfway. We landed in Eno Terra in Kingston, and it was absolutely wonderful. All local food, house made bread and pasta, amazing cheese and charcuterie tray. I had the best gnocci of my life- pillowy soft, melt in your mouth with pancetta and carmelized cauliflower. Amazing atmosphere. It is not a BYO but they did have a very good reasonabble priced wine list. We had an amazing bottle for only $40, and there were a few options in the $20s. It was only about a 45 minute drive (from Ambler).
I also heard good things about the Blue Bottle Cafe, also in that area. It is a BYO (we were specifically looking for a bar) so you might want toi check that out as well.