Mosaic reworked

I just read that Mosaic is getting reworked:

Blizzard also confirmed that Mosaic is being removed from ladder ahead of a redesign, with further item rebalancing and additions planned depending on the expansion’s performance. source

As far as I know, these changes usually don't effect existing items. Do you think this well be the same here, too?

Most likely.
I doubt they'd retroactively kill all existing Mosaics. They generally haven't done so in the past for other items. Neither for the .08 goodies back in LOD nor just now for sunder charms. Exceptions are typically limited to identifiers, rather than stats, such as existing Hustles getting renamed or to set boni which I believe were treated as "item/roll independent" as well.
So yes, stockpiling those could become a solid money-maker.

However, if you look at Blizz's list of known issues for RotW, it includes one about Mosaic that very much sounds like they're not removing it from ladder in the sense that "Mosaic will disappear" but rather in the sense that "you can make them in non-ladder, too" (which you currently can't though, that's the listed known issue).
So if that's the case, you'll get the opposite effect by stockpiling as they'll become more readily available to anyone and drop in value.
That's the gamble for ya.

Thanks for your Insight!

I actually wasn't planning on hoarding but was concerned about the 2 I built myself and was wandering, if I should get rid of the bases I collected. Well lets see what they come up with....