For a fresh VyOS installation the following conntrack helpers are enabled by default:

conntrack {               
     modules {             
         ftp               
         h323              
         nfs               
         pptp 
         sip  
         sqlnet
         tftp  
     }         
 }

In order to follow the design of offloading options (default disabled) I think that also ct helpers should by default be disabled and that the admin must explicitly enable whatever helper they want to use.