if you look at the LFIB (show mpls forwarding-table) you will see, that the outgoing label for the neighbor Loopback is imp-null, i.e. it will be an IP packet leaving the respective router (PHP - penultimate hop popping).
Thus LDP between directly connected neighbors will only involve IP traffic and not be labeled.
the LDP convergence is not affected by the existance or non-existance of imp-null label. The LDP session is not recreated if a label is withdrawn, but only if you lose the link between the neighboring routers.
To avoid even this use targeted LDP sessions, which are configured like this:
mpls ldp neighbor 18.104.22.168 targeted ldp
ip address 22.214.171.124 255.255.255.255
ip address 10.0.0.1 255.255.255.0
mpls mtu 1512
Or use MPLS LDP session protection:
mpls ldp session protection
There is no dead time of a tunnel involved in convergence. OSPF relies on link local multicast (126.96.36.199 and 188.8.131.52), which is not labeled. So your routing convergence has nothing to do with labels at all.
In case you want to reduce the number of labels announced you could use conditional label advertisement:
no mpls ldp advertise-tags
mpls ldp advertise-tags for 90 to 91
where 90 and 91 are access-lists (90 for which prefixes, 91 to which neighbors).
Be extremely careful though, because this could destroy LSPs necessary for your MPLS VPNs and the like.
So in brief: There is no drawback of the implementation between neighboring routers.
This document is an early notification of a behaviour change that will be introduced in IOS XR release 6.5.
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