There are already systems out there for gamers to play tabletop games on their PCs, and these systems are generic - allowing players to use their own rules, measures, etc. While they're not tied specifically to licensed IPs like Warhammer Fantasy or 40k, they allow people to play them. And this brings me to my answer to your first question:
Can we compete without an IP?
My gut reaction is no. There are already PC/Online strategy games out there, both Real-Time and Turn Based, and unfortunately, they probably have a much larger budget and design studio to play with. Furthermore, there are already perfectly good, "static model, base, and dice" games out there which can be played on the tabletop. So who are you catering to? Because the generic game systems cater to the guys who want to play their tabletop games on the PC, and the other stuff caters to the strategy players.
Of course, you have to understand that I'm the kind of guy who doesn't "get" why people are so in love with online card-gaming, like 'M:tG Duels' and the new 'Hearthstone' game. Particularly with the "online only" games like Hearthstone, which don't have an 'in the flesh' proxy for it.
What Features to Include
You really need a "hook" for this. The solid models and dice will do it for the "hipster-esque" people, because it's "vintage", but it's not going to convert the guys who are already playing TTGs or online RTSs. You need to do something that will bring in those people, beyond just "hey, Warhammer is expensive and this game can be played anywhere".
Personally, if I were doing it, I'd make it 'Free to Play' (with such a simple layout, there's no reason why it shouldn't be), and then do the things that traditional TTGs can't:
1 - Play By Post: traditional TTGs take hours, and RTSs can only be played in single-sessions. Let players fight at their own speed, maybe with a time-limit of some kind (if you don't take your turn within 24hrs, you forfeit the game, etc - bonus points if you let players select this speed themselves when choosing opponents).
2 - Give units a game-to-game progression: Let players "collect" any of the different armies. They start out with a Commander and small selection of units, but as they play, they accrue experience points to unlock new units, as well as having their units become more advanced. Maybe each unit gets a "Heroic Level" as their ultimate upgrade, becoming some kind of named unit which features in the game's lore. Something like:
Eld Scouts -> Eld Marksmen -> Eld Elite Snipers -> Talons of Endrasil
Let players move back down through these levels at will though, so that they can play smaller/basic games if they want. I hate that as I play 'World of Tanks', the more I advance along the tech tree, the "higher tier" my games become - I start off at Tier 1, but now that all of my T1 tanks are gone, I can only play T6 games.
3 - Let players interact with the community: Again, RTSs and TTGs both only allow you to interact with your immediate opponent. Allow players to do stuff within the larger group. I wouldn't want to see MMO style 'factions', because I hate being locked into a situation where I might lose because my faction attracts all the noobs (alliance, in WoW), or be locked into playing a single army. However, maybe players can farm out units they aren't using to be "Mercenaries". Those Mercenaries would gain extra experience, but there would be some risk involved (maybe if they suffer casualties, you have to pay something to recover them). Let players set a price, and a minimum rank required for other commanders to draft them. That would also let newer players who haven't unlocked the more advanced tiers of a unit, a chance to use that unit their games if they pay the amount to hire the mercs.
Auction Houses for items on your commanders, and options to play allied games or even huge multi-player games (perhaps organized by the people who run the game).
5 - Bigger tables: This kind of goes hand-in-hand with the multiplayer thing, but currently, TTGs are limited by space. Games are usually on 4x4' or 6x4' tables, and I can't run anything too much larger without clearing out the garage. But, when I did clear out the garage, the game was awesome. Do something like that for your players. Especially if you have play by post, and the players can afford to spend more than a 6-turn game getting into combat. Give them big battlefields to explore - with areas which grant bonuses or rules, and scatter some loot around for them to find.