An incoming update to ardour will not have support for LV2 plug-ins due to the removal of slv2 from its dependencies. This is a result of an API/ABI incompatibility between the latest releases of the Redland/Rasqal/Raptor suite that we ship and Ardour's internal supported versions of those libraries, which SLV2 depends on. This is also primarily what caused the build failures and runtime segmentation fault that you may have experienced.
Upstream will not be updating its codebase as all efforts have shifted to version 3 of the DAW, which will do away with SLV2 altogether (and possibly adopt other implementations of the LV2 standard, if at all). Currently, no-one has submitted a patch to address the issue. Compatibility packages are not possible to provide in this case, and as such, we have decided to drop LV2 support from our Ardour package. Users can still use LADSPA plug-ins or, which is probably already a popular workflow, resort to other LV2 hosts with the help of jack and its routing capabilities.
Update: LV2 support is back in. Please see bug report for details on how this was fixed.