For lists, vNext MvxBindableListView has supported ItemLongClick for a while anyway - see
Note that this binding hooks into the ListView's ItemLongClick rather than into LongClick
Using this in your axml, you should be able to just do:
<Mvx.MvxBindableListView
android:layout_width="fill_parent"
android:layout_height="fill_parent"
local:MvxBind="{'ItemsSource':{'Path':'GroupedList'},'ItemLongClick':{'Path':'JobSelectedCommand'}}"
local:MvxItemTemplate="@layout/listitem_job_old"/>
If this doesn't work then please fire a bug report on Github issues.
If you wanted to do your custom binding on a generic (non list) View, then your code would need to switch to ICommand instead of IMvxCommand, and you also couldn't really pass in the Item argument - so you'd need to just use MvxRelayCommand on the ViewModel.
I've added View-level LongClick support to the issues list - https://github.com/slodge/MvvmCross/issues/165
But for a ListView it is probably the ItemLongClick you are actually interested in