I own both Legacy and DCS, and would recommend purchasing both (if funds allow) to maximize the operational aspects of both systems.
However, I would like to offer some comments regarding a few of the posts above:
You can incorporate conventional Control by using the remote to control the transformer. Lionel has the zwl with is a remote Control transformer. They also have tpcs which are another remote control transformer.
Using DCS's variable channels, conventional control is included without the requirement for any additional purchases at all.
If Lionel posted the codes for Legacy, couldn't MTH take advantage of that, in a future release?
Yes, absolutely, using current DCS hardware.
Yes DCS will run it, but only after you buy Lionel's TMCC/Legacy components, so you end up buying two systems
Actually, all you need is a TMCC, Legacy or Base 1L command base. The Lionel Legacy Cab-2 is only required if you desire to operate Legacy-only features. The difficulty is that, at present, I don't believe that any command base is available for separate sale, unless one purchases a used TMCC Command Base.
upgrades for Lionel over the internet and are far simpler than using MTH's system
Not really "simpler". The DCS upgrade is a one-step process. After downloading the free software from MTH's web site, each DCS component is upgraded directly.
Upgrading Legacy requires two steps. First, updating a pair of (extra cost) hardware modules with the software. Second, then plugging the appropriate module into each Legacy component and doing the actual upgrade.
right now it looks like MTH is going to rely on Dave Heikel to support Legacy commands via the DCS app
It only "looks like" that if one chooses to see things that way.
Regardless, that is not necessarily the case and, AFAIK, there have been no credible statements in that regard.