I cannot comment on Elinos as I do not know it.
In general I would tend to stay away from "proprietary" linux based real-time solutions. First you are locked in with the supplier; second, many suppliers run sooner or later in the situation where they cannot keep up with the kernel development speed with their modifications, with the result is that their real-time version is discontinued. This could be observed a lot in the past 10 years.
In my opinion it's better to stay with a community. Companies go out of business and a user is left with nothing, no support, no code, no contacts; communities stay alive as long as there are users and contributors, communities might dissolve, but at least you have some code and email addresses of real people.
As far as RTLinux is concerned, I have to mention that I used it several years ago. Then, one used to download a vanilla kernel for which an RT patch existed, patched that kernel, compile and install. The patch created rtl.h and other header files. All you needed to do is write your application as one or several kernel modules, compile them, then ismod rtl.o and other things you might need, then insmod your application's modules.
There are two things to consider. First, if you write your application in kernel code, you are bound to the GPL, keep that in mind. Second, it is much harder to debug an application in kernel. That said, perhaps a "modern" Linux kernel compiled with high resolution timers and with the PREEMPT patch applied would do the job. More information on https://rt.wiki.kernel.org/index.php/Main_Page
. Perhaps rethink you real-time requirements.
If you really want RTLinux/GPL, then get in contact with Nicholas McGuire (www.opentech.at
) or one of the poeple at http://rtportal.upv.es/