I don't disagree that it might be smart for Vegas to trade down, but the problem with trading down is that someone has to want to trade up.
Nobody is giving up a lottery pick next year for the privilege of moving up a couple spots unless there is a franchise-changing player available at #1. I don't think there is an obvious franchise-changer like A'ja, Stewie, or EDD in this draft.
And if such a player is available, why is the team that holds #1 ever trading that pick?
Indiana finished dead last and 9 games out of the playoffs. They have to know that they are likely to be in the 2020 lottery and more than 1 great player away from contention. Why would they ever give up their 2020 1st just to move up 2 spots?
I gave examples of possible trades, from Las Vegas's perspective.
From Indiana's perspective, the team needs help almost everywhere...shooting, playmaking, presence, etc. With Kelsey Mitchell and Victoria Vivians, the team has two pieces for the future. But Candice Dupree and Cappie Pondexter are well on the downside of their respective careers, and Natalie Achonwa is a nice roleplayer but not a top three player on a good team.
I will give you two scenarios for Indiana.
First scenario:
Let's say that Oregon's Sabrina Ionescu declares for the draft. Indiana views her as a PG/playmaker in the Lindsay Whalen mold for the next decade. That would be a player for which to trade up...and Indiana could demand another player from Vegas as part of the trade who can help the team (e.g., Dearica Hamby) if it would surrender its lottery pick in 2020.
From Vegas's perspective, the team has Kelsey Plum and Moriah Jefferson, one of whom is sure to have All Star potential. And the team really wants Napheesa Collier at the four, next to A'ja Wilson. This way, the team gets the player it wants in 2019 and a lottery pick in 2020.
And from Indiana's perspective, it gets a potential star (and box office draw) in Ionescu, with its young core.
Second scenario:
Sabrina Ionescu does
not declare for the draft. Vegas offers the #1 pick in 2019 plus Moriah Jefferson and Dearica Hamby for the #3 pick in 2019 plus Indiana's 2020 likely-lottery pick and Victoria Vivians.
Vegas finally has a starting lineup with balanced backcourt and frontcourt scoring and a great young core going forward -- Plum, McBride, Vivians, Collier, Wilson.
Indiana gets its point guard (Jefferson) and center (McCowan or Brown) of the future to pair with SG Kelsey Mitchell, while getting Hamby as a forward.
For both scenarios:
Alternatively (and in both scenarios, actually) Vegas could simply exclude Hamby from the trade and add a swap of picks in 2019, which would still give Indiana lottery pick in 2020...but with Vegas getting the ability to choose between the better of the two picks.
Additional note:
I only did the analysis for Indiana. Obviously, there may be another team looking to move up in the draft this year for which a trade package could be presented.