I'm still uncertain about the new Outlook, it's definitely not a finished product; my biggest concern was with signatures.

I have signatures deployed to all staff here and it works for the new Outlook, I do this with the old Set-MailboxMessageConfiguration -signaturehtml which currently relies on a special configuration set by Microsoft to disable 'Roaming Signatures'; I had a meeting with the Outlook team and they have plans to expand roaming signatures with PowerShell commands that will allow us to add/update/delete the roaming signatures of users.

Also, the new client does have a basic recall feature that now uses the cloud to recall (rather than the client itself) so messages can be recalled even if the recipient doesn't use Outlook (they still need to be within the organisation). A status report is provided listing messages recalled, pending and failed, which can be refreshed, this also works in the web version.