You can rely on dojox/mobile. DojoX will indeed disappear from the Dojo Toolkit in 2.0, but most matured (and probably maintained) modules will be pushed to the dijit/dojo library. I quote the reference guide:
In the future (Dojo 2.0), the DojoX package and namespace will
removed. Sub-Packages and modules will be either integrated into the
Dojo Core, Dijit or separated as their own stand-alone package. For
the 1.X code stream though, in order to ensure backwards
compatibility, all these packages are contained within the dojox
namespace and package.
If we look at the explanation of Mature, we can read the following:
This package or module is considered mature and is being actively
developed and maintained by committers within the Dojo Toolkit. It is
expected that it will persist into the foreseeable future.
Source
And if you look at the link above, you will notice that dojox/mobile
is categorized as mature.
Another reason you can rely on it is that IBM (which can be considered a pretty big company and committer to the Dojo toolkit) also relies on dojox/mobile
for their mobile product called IBM Worklight. If they rely on it, then there's no reason you couldn't.
I don't think it will be easy to start from the same code base and swap out dijits
for dojox/mobile
components. Usually mobile app development requires an entire different strategy than web applications. You will probably have to split certain things into multiple views and some dijits may not have a mobile alternative.
You can probably re-use most of your utilities and business logic, but I think you will have to start from scratch again if you want to write your view(s). But I'm not really an advanced mobile developer.