I'm all for adding the Land Speeder Storm to the Scout formation (Frankly, I'd like to see it replace the Rhino/RB options). It's different, and it allows the Scouts to move farther and scout ahead. Just need to talk to O-man about some 3d work.
I think the Land Raider Redeemer is a bad unit for Epic, as it loses all it's range for a (admittedly nasty) 15cm AP attack. The Salamanders don't need to be screwed that badly, they're already underpowered for ranged weapons as it is.
Sternguard/Vanguard vets I'm less sold on in Epic, although replacing 1x missile Launcher with 2x plasma guns and FF3+ would be simple enough to do.
Not sure about stats for the Vanguard, they aren't quite as beefy as Worldeaters. Maybe just Power Weapons (Macro-weapon, Extra Attack (+1), just like the Terminator statline). First Strike is too much.
The other question is how to fit them into the army: As a single-unit upgrade to a Formation, or as a formation-wide upgrade. I can make arguments either way. For example, the Ultramarines First Company has ~80 suits of terminator armor, and 100 members. The (epic) makeup could be something like 3x Terminator Formations (20 Marines each), a unit of Sternguard vets (20-30 Marines), and a unit of Vanguard vets (20 Marines). That's IF you put all the veterans in one place (as formation upgrades). I think a Chapter would be better served by spreading the veterans out (so they'd be a unit upgrade).
The answer is which works better in-game: No veteran Marines in power armor, veteran Marines as a unit upgrade, or veteran Marines as a Formation upgrade?