Well, to answer this you really need to consider what makes other footslogging armies feasible.
Orks are dirt cheap and have supportive leadership tricks to prevent breaking, all their special and heavy guns are assault. Have special cover generating tricks.
IG are dirt cheap and have supportive leadership tricks to prevent breaking they either have assault guns or the ability to take multiple Heavy guns with good range. Have special cover generating tricks.
Eldar are quite cheap and have move and shoot shenanigans and also heavy weapons that are treated as assault. Have psyker tricks for support.
I think those three are really the big 'footslog' armies out there.
Nids are probably out there too, and they get by with leadership tricks and dirt cheap and troop generating tricks - but they are a special case swarm concept and I wouldn't want to emulate their methods.
As far as 'cheap' goes we do pretty well as we cost equivalent to the Guardians.
We lack leadership buffs though.
We also lack movement tricks.
We also lack the long range and the assault weaponry options of the big three.
We also lack the ability to generate any cover.
Also, our Wyches desperately shouldn't try footslogging, so we're obligated for Wracks as assault support.
That's why we don't really footslog, if we try it, Wyches are basically out, and the Kabalites are kind of 'meh' at the attempt.
If I wanted to make us able to go footslogging I'd probably a couple of things;
1. the ability to take multiple assault weapons (if I could field 2+ Blasters or Shredders in a squad it would dramatically increase the potency of the unit) and/or the ability to mount lances on assault platforms of some stripe.
2. Something to increase our survivability. Maybe an upgrade for a portable night generating field that would give us a stealth effect? Or a leadership boosting/control effect? We need something to make it viable to try to march our guys across the field, and we certainly don't have it currently.
I think the Webway idea is interesting, as it might allow us some interesting objective claiming trickery that we would lose by giving up Raiders/Venoms. I also like it because it focuses on maneuverability, and I think maneuver and attack power are the two bywords of DE design.