There is no MetaROUTER for RouterOS ARM platforms. Do you see a "/metarouter" tree on the RouterOS CLI for your AHx4, or a "MetaROUTER" config option within Winbox for this model? Thought not. You might be able to eventually build OpenWRT for the SoC in the 1100AHx4, but it is going to have to run bare-metal on the hardware, not virtualized.
The "v1.2" patch in the Wiki docs is YEARS old, and the "1100" model they reference is the single-core PPC version, not the dual-core PPC and *certainly* not the quad-core ARM one. None of the code in that patch is going to be of *any* use to *anyone* in bringing OpenWRT to this model. And besides, the patches that MT released for the 1100 way back when were only useful insofar as building an OpenWRT image that could boot *within* RouterOS' MetaROUTER, not bare-metal.
Without simply waiting for OpenWRT/LEDE developers to officially support this hardware, your best bet is to grab the latest RouterOS GPL kernel patches from MikroTik, and then work to integrate them into OpenWRT yourself. And, again, to be clear, all that this gets you is a build of OpenWRT that you can use on an 1100AHx4 INSTEAD of RouterOS, not *in parallel* with it.