Just curious since this is your first post, you an Eagles fan? If so, we have like none before you, lol.
Other than Peters the Eagles overhauled their entire line last year. They changed from a traditional man blocking scheme to a zone blocking scheme when they hired Howard Mudd at the beginning of last season as the O-line coach. He had the same role for Indianapolis for many years, though blocking for Peyton is a lot easier than blocking for Vick.
The Eagles started a rookie center (Kelce), a rookie right guard (Watkins), a "street" free agent at left guard (Mathis), and moved their former left guard out to right tackle (Herremans). In addition to this Vick was given more responsibility to call out blocking schemes, possibly too much to throw at him at once.
By the latter part of the season the Eagles line was pretty good. They were particularly good at run blocking in front of Lesean McCoy, not quite as good at pass blocking.
Keep in mind that Vick is left-handed, so Peters was not playing blind side, even though he was on the left. Herremans protected the blind side reasonably well. Herremans can also play the left, so (at least for when Vick is healthy) the Eagles are looking to add either a non-blind-side left tackle or a blind-side right tackle.
McNeil is one option, but his health is highly questionable to say the least. Might not even pass a physical. Bell is a possibility, but apparently is after a much larger contract than his play deserves. Kareem McKenzie is washed up, no point on signing him. And that's pretty much it for free agency.
The draft has some possibilities but it is not likely to produce a player who can be trusted to start right away, drafting from the 15th spot.
So, at this point, they have to be looking at some trade possibilities.
Welcome aboard either way.