Currently DMC 1 and 2 are on the switch. While it isn't confirmed, DMC3 is likely to come to Switch in the next few months to complete the collection. DMC3 is typically agreed upon to be the best all-around title in the series when it comes to both Gameplay & Story, so many would be quite happy to see it hit the switch.
However, the pricing for the current DMC titles on Eshop definitely stick out even to the most hardcore DMC fans. $20 for each title if DMC3 follows the trend, makes the Switch HD Collection $60 ($55 if you grabbed DMC1 on sale for $15 awhile back). A high price to be sure, considering the MSRP of the same collection is $30 for all 3 on PS4/X1/PC and the switch versions thus far offer no new features.
But what if Capcom followed a recent offering they did for another series? Resident Evil 5 & 6 are currently 33% off if you own RE0, REmake, or RE4 digitally. They even put these titles on sale when this promotion was first offered. Allowing you to grab all of the current RE games for the same MSRP as they are on other consoles.
A similar promotion doesn't seem outlandish for the DMC series, even if DMC3 is a fan favorite that would likely sell $20 on its own. The best outcome (albeit very unlikely) would be "If you own DMC 1 and 2, you get DMC 3 for free" with a 25% off sale for each title making the price comparable to the other system's MSRP (If you bought them at $20 each you did keep to play them already after-all and you'd still be getting 3 free). The realistic outcome would just be to have some sort of offer comparable to what RE5/6 had.
I know a lot of this relies on how "nice" Capcom is feeling (They don't have to offer any sort of deal/discount after-all), but i'm curious to see what the expectations are from Capcom & Switch fans here. As I know there has been a lot of criticism on their current switch offerings, especially when it comes to higher price with no extra features to justify them in a lot of cases. So something like this even if it's not perfect is at least something that gives off a better image (I personally even as a big RE fan, refused to buy the ports until the prices lowered and I typically grab any RE port Day 1).