...I would like to make a request if it is even possible. I would really like a way to run Inkscapes cool bitmap filters inside native GIMP itself. Yes, I know we now have a tool to do so via Shellout, but, why not port this ability within GIMP itself?

As far as I know, the bitmap filters provided in Inkscape should be ordinary plugins written in Python. Hence, I think the simplest way to port these filters from Inkscape into Gimp essentially consists in converting and reshaping their source codes, by replacing the exclusive Inkscape procedures with the corresponding ones of the Gimp PDB which are aimed to do the same tasks; whereas there will be no necessity of modifying the native Python commands and snippets instead, as they ought to be perfectly recognized in GIMP too.

For whoever is skilled in programming with Python, a work like this should not be particularly difficult to do, considering that it only takes some patience and time.
As for me, only recently I have started studying the Python language, so unfortunately the operation in question is not in my ability for now. Nevertheless, I am pretty sure that some users of this forum (especially those who usually post and share Python scripts) might be able to perform such a kind of conversion, at least with regards to some fliters among the most significant ones whose functionalities are not implemented in GIMP yet.

Which Inkscape tools or Effects, Lyle?

The vast majority of Inkscape filters appear to be direct implementations of SVG filter effects written in XML. Their functionality already exists, for the most part, within GIMP; it is just that the names are different and the parameters arranged differently. (GIMP predates the standard so it does not comply with it exactly; sometimes for better, at others for worse).

Note that once GIMP is completely converted to GEGL (planned in 2.10), support for SVG filter effects will be built in and replicating Inkscape filters exactly should become trivial.

If there are specific filters you'd like to see converted, please point them out. It appears that most of them are already available directly through GIMP operations.

I really like Marble and Refractive Gel A Saul; I know that similar results to Refractive Gel A can be done by Script-fu, but not quite 100% to my taste. Have not seen 3D Marble implemented at all; Mother of Pearl either. Others I like too, but don't use nearly as much as these three presets.