Hey, what's the mod-colored R1 \| key in the base kit for? Split backspace is already covered by the alpha-colored one. The most common split backspace setups are \|, `~ and \|, Delete. Mod-colored \| would be useful for a `~, \| setup, but I don't think that's very common at all (at least not enough to warrant including that key).
Would you consider changing one of the ISO alpha keys to avoid having a duplicate \| legend? I've been hearing complaints about these recently. You can either change the R4 key to <>, or the R3 key to #~, based on what you prefer. R4 <> is better objectively speaking (details
here), but many people (mostly ISO-UK users) seem to prefer R3 #~.