This may not work for you and I have not tested this, but you could try adding a parallel block to your workflow. Then for the part where you want to wait for item update, use the Run If action. This allows you to choose not equal to and other options depending on the field type.
@jgoudy
Yes the o365 action is a bit limited and no real further improvements will be coming.
Your best bet might be to migrate your workflow from Nintex in 365 to a Nintex workflow cloud (NWC) workflow. You can still leave your Nintex form on the list in Office 365 if that is relevant.
The new action in NWC for SharePoint Online, 'Wait for event in list item' does support the does not equal conditional operator.
Microsoft will eventually shutdown the SharePoint 2013 model workflows and we'll have to migrate to NWC then anyhow, if you are developing new workflows good time to start looking at developing these in NWC connected to SharePoint online.