So about whether Z-A is set in present vs past. The very first info we got from Legends Arceus site said
>Survey, catch, and research wild Pokémon in a long-gone era of Sinnoh to complete the region’s first Pokédex.
Meanwhile Legends Z-A site says
>A new adventure awaits within Lumiose City, where an urban redevelopment plan is underway to shape the city into a place that belongs to both people and Pokémon.
There's already a difference: LA openly says its a game set in past Sinnoh, meanwhile ZA just says Lumiose City. Obviously it doesnt state what time period it is but considering the teaser showing us modern city aswell as sketches of modern dressed girl we could assume it is present. What would be the point in hiding the time period from fans when majority already thought its going to be past because Arceus was like that?
Then there's the logo: Arceus being old style paint brush-like while ZA looking modern and electronic. Not to mention Z-A directly follows XY naming scheme whereas Arceus isnt following Diamond, Pearl and Platinum titles.
And finally the synchro machine symbol on the map that was shown in the reveal teaser (pic related). As far as we know its a recent discovery in Blueberry Academy so the game should take place not only after XY but also after SV aswell.
It could go either way but as of right now im team present.