At least from what I've read, there was no visible stale negation in any of the demos we've seen. It could just be irrelevant to the Sandbag room, or possibly only applied to knockback instead of damage, but as of the moment, unless I've missed something, that mechanic doesn't currently address the spam issue in Smash4.
That said, making stale moves significantly more penalizing would discourage spam like that. Though that's not really relevant to the air lag discussion.
On the subject of "lower aerial lag gives everyone more options", that's not necessarily true. Using Mac as the poster boy for "no aerial game", as I've mentioned before, if you make aerials too favored in terms of ending lag, then anyone lacking strong aerials for whatever reason will fall hard out of the meta.
The two attack styles need to be balanced around equal viability, and without wavedashing or similar mechanics (pivots may function as a similar approach option mechanic), the "fastest" way to approach on the ground is a dash, which locks you into exactly four options: Shield, Dash Attack, Grab, or Jump. People said the shield drop on the demo was too quick, which made dashing, shielding, and then attacking from shield the preferred strategy. Without wavedashing or in Brawl-esque mechanics, the dashing player either has to jump attack, grab, or go into a sometimes very telegraphed and sometimes slow dash attack. There are, of course, exceptions, but as a general rule, no dash attack is even remotely safe when shielded, while many aerials can be canceled with an extra jump, or can avoid commitment with low landing lag or L-canceling or what have you.
There are ways to make the grounded approaches more viable, rather than simply making the aerial approach consistently better. Of note are to either to change many characters dash attacks to have quicker startup or lower endlag (or some combination of the two), or to make shielding a laggier and more variably punishable technique like it was in Smash 64. One thing that is often overlooked (on the landing lag debate, not the endlag debate) is that landing lag has little to do with purely aerial combos or chases, and is entirely related to the end of an initiation or combo, where you are returning to the ground and use an attack there. Reducing LANDING lag makes a failed initiation less punishable, which not only devalues the decision to defend, but allows the attacker to almost immediately resume their attack. Reduced ENDlag makes combos connect easier and faster, which seems to me to be what more people are clambering for in general.
So, while I would easily support a selective reduction of aerial endlag as a balancing mechanic to give characters potential for aerial combos as a followup to a grounded launch. However, the reduction of aerial landing lag simply makes a wiffed attack less serious for the player who missed, and while that sort of attack is safer than a grounded equivalent, I can't see that sort of metagame working for much more of the roster than it did for Melee's. And I'd really love to see character validity spread across the board instead of limited to less than a quarter of the roster.