We have several mitigations on the scanner side. One of these is scan queueing. If you start a lot of scans, you should see corresponding info messages that not enough RAM is available and that scans are queued. If you want to get technical, you can adjust the limits for the scan queue in /etc/ospd/ospd.conf.
Related, there exist other scanner limits that you can tweak, see min_free_mem and max_sysload from the scanner preferences, alternatively these can be set in /etc/openvas/openvas.conf.
There are some remaining problems, for example the vHost and CGI caching described in my post here. These could be classified as bugs, and we are currently working on a new scanner generation to solve these.
Last but not least, other system services besides the scanner may use large amounts of system resources, for example gvmd. This can happen at short notice, giving the scanner little time to react. We are aware of this, however improvements are not trivial in this case.
In any case, if you want to help out, feel free to contact our developers via our GitHub projects!