I played some Swain on the PBE today because I really like the character's feel pre-update and thought I'd see what they changed to make his gameplay more strategic. I have to say, I was disappointed. Although I do like the buffs to his E (damage amplification 20% at all levels now and higher AP ratio, for reference), the changes to his Q would seriously ruin this champion for me if they went live.
First off, the cast range for Q makes Swain get close to his enemies. Very close. In the past, this wasn't a problem, because the Q tether would stay on enemies that decided to try and punish Swain. Now, if Swain tries to lead with Q in order to make hitting W easier and the opponent turns on him, he's hosed, since they'll very quickly escape the Q, which means he's caught out with only E and (maybe) R. This allows for an easy trade/all-in kill for assassins and mages alike.
Basically, the fact that Beatrice's threat range has been reduced makes Swain much weaker against the type of champions he formerly countered: assassins. The field is easily avoidable/escapable by even low-range dashes/blinks, leaving Swain without one of his key damaging and soft CC abilities. Before, he'd have his enemy right where he wanted them if they turned on him, since Q would still slow/damage them, as Swain would almost certainly be within Beatrice's range. This, combined with the fact that the scaling buff was redacted, means the change is a direct nerf to Swain's dueling, since nobody with half a brain will sit with Beatrice for more than 2 seconds, and the cast range makes the old Q->W combo incredibly easy to predict and avoid unless Swain flashes, meaning he also won't be able to lock somebody down in Beatrice's range for the full duration. In addition, Q now has a longer cooldown at all levels.
Now, the buffs to Swain's ult are nothing to sneeze at. Reducing the mana consumption at higher levels and adding 2 ravens will really help Swain do what he was made to do in teamfights. However, the goal of Swain's character design is strategic power and diversity. While I think Swain could certainly benefit from a zone-of-control/damage ability, the zone is too small for Swain to consistently deal damage against enemies that are actually wary of his harass/all-in patterns.
Some possible solutions would be to do what Beatrice already does in live: make the tether range longer than the acquire range, so that Swain doesn't lose a quarter of his offensive kit when people dash, blink, or just walk away. The AOE could also be made bigger. I think the main problem is that, at least during the lane phase, the Q changes are a nerf to Swain's already-tricky early game, while only providing a bit of extra lane push (which Swain is already very good at once he gets ult). In addition, the fact that the Q no longer has an instant tick on cast makes it harder to last-hit with, and makes champions take less damage overall during trades.
TL;DR: Q has less damage (due to no more instant tick on cast), and much less threat range (enemies don't get punished for all-in), with the only positive change being that it can switch targets once one dies, which will only ever come in handy on minion clear, which Swain's ult already handles. I'm not a high-elo Swain main, but I don't think this helps Swain's strategic play/diversity at all.
As a side note, the W setup time feels a split-second longer for some reason. I have the timing pretty well-ingrained in my head because of the memorable sound effects, and it just seems late every time.