However, the default setting for most nodes is 300MB, so we should be a little concerned if we approach that size on average across the network.
There is no danger except a "danger" of large fees. Bitcoin Core will remove the low-paying transaction from the mempool so there is no way the memory gets exhausted. And actually, we crossed the 300 MB mark. My node (configured up to 600 MB) is currently at 490 MB usage.