Sadly, they're going to be mobile games. I'm not really surprised since Japanese gamers have essentially moved their daily gameplay activities onto their smartphones (case in point: Super Mario Run). Console gaming seems to be slowly becoming a thing of the past with them. It's disappointing, but what can you do? About ten months ago, I had my hopes up that a Wild Arms 6 would come to fruition after series creator Akifumi Kaneko hinted about a "20th anniversary meeting" (gematsu.com/2016/01/wild-arms-…), but that won't be the case. I really need to stop holding out hope for these things.
As for Arc the Lad, the plan is to continue the story from the main series (I'm assuming that means after III). I haven't played III yet (finished II last year), and even though Arc the Lad was an interesting curiosity that deserved better than it got, the fact it's going to be on mobile doesn't really help.