This passage jumped out at me
I think you've got it backwards. Last season I think Randy Moss has kept defenses honest and that he opened things up for Welker and Gaffney, not the other way around (Jackson's yet to do anything of course and Watson and the TE position's health and strength were at issue last season as well).
The opposite could hopefully be true this season though. One of my concerns is that we had the opportunity to do exactly what I think you're advocating here last season and McDaniels chose not to. Hopefully that changes this year.
Jackson isn't so much replacing Stallworth because aside from early perception, Stallworth never had a major impact (well, aside from the Dallas game, which I initially took as a sign of things yet to come, but that never materialized).
I think Defenses will hapilly give up the short pass to Welker in the hopes of preventing a deep pass to Moss - a bend but don't break scenario for them - though they will have to devote coverage to containing him. So I don't see Welker opening things up for Moss - just more that Welker gains from the focus defneses place on Moss.
Whether Gaffney, Jackson and the other receivers will make defenses pay for their attention to Moss and Welker is the real question in my eyes. Jackson will have major opportunities to get deep with limited coverage while defenses focus on Moss. He could hurt them and thereby command more attention himself - thereby benefitting the rest of the receivers, including Moss, in particular on obvious deep passing situations.