Okay here's how to refine the idea and make it REALLY interesting. At least in my humble opinion. First off, have this SCP usable from the other sideas well, as in, entities can access the Foundation universe. Which has several disturbing implications, which I'll try to list. So the most obvious and immediate idea that might occur to you, is alternate universe versions of SCP's like 2399, 682, 106 and 173 coming through. I'd recommend against this, but it does give you a way to also introduce related SCP's and new original concepts to the setting.
The next is the idea of Multi-Universe entities, empires and factions, trying to get into our reality. Things like Lovecraftian elder gods peeking in on us, like viewing an ant farm. Powerful factions and states like alternate universe Nazi Germany, ruling the world, The south winning the civil war, a universe with SCP-1000 still in-charge or something similar to the combine of Half-Life and Burning Legion of Warcraft. Seeking to control, conquer and expand their influence. As such the neutralisation of this SCP would be a high priority. It could be speculated that a lot of SCP's entered our reality this way. Also it'd make sense if there was similar barriers/perimeters in other universes, stopping foundation personnel from entering and investigating. As such this SCP could in fact, exist in multiple realities at once, and be indestructible. Requiring a facility just to house and seal off the threat, it poses.
I'm not sure how you would use it yet. Maybe a device like a stargate dialling system or using a switch/lever to shift it?
