I'm not betting on a remaster announcement. This isn't the first time they've made an event out of a major late patch to WC3; they were patching steadily in 2016 (1.27) and 2017 (1.28), sussing out some OS compatibility and adding options for windowed fullscreen, although much of the attention surrounding these patches was directed at the Chinese market. Back then, people were speculating about a remaster as well—and it's true that active support for the game lays the groundwork for the SC:R model where the remaster was really a fresh graphical coat of paint with modern Battle.net integration, totally interoperable on the fly with the base release.
But native widescreen support has been such a large and longstanding request that, along with all the unexpected UMS improvements, I can absolutely see Blizzard deciding that an exhibition event like this one is a proportionate marketing push for 1.29 and only 1.29. We'll get a remaster Soon, I'm sure, but I'm not convinced this patch and exhibition provide the grounds for an announcement.
For comparison, leading up to SC:R there was considerably more activity in the air among veteran players, specialist sites like Team Liquid, and e-sports organizers, all flying out to Blizzard or being briefed under embargo. WC3's scene is smaller than BW's even now, but if a remaster announcement were imminent, I'd still expect more of a background hum leading up to it, reaching out to more of the Blizzardsphere than just the remaining WC3 community. I really think this may just be a 1.29 showcase and would advise against expecting more.
I'd love to be wrong. (But I also don't see a WC3 remaster as all that urgent once widescreen is in; this game has aged very well, and the kind of work that the classics/remasters team was assembled to do—recover original code and artwork and spruce them up for HD—is something you'd sooner expect to be directed at D2.)