we want to connect ASR1006-x directly to spine, and make asr1006 as a special border leaf , and connect WAN-VRF to our different customer on ASR1006 interface faced to remote customers,we now just have 1G line from ASR 1006 to Nexus 9508 spine.
If we are talking about ACI fabric and you want to connect your border leaf it has to be connected to the leaf switches since the spine only supports leaf switches connected to them. Now if this is FabricPath which there is limited amount of 9K that supports this, it should not be a problem.
we are now testing spine leaf vxlan technology, spine is 9508 leaf is 9300-ex , but for wan,we have ASR1006, we have tested asr1006 connected directly to spine, and it is working,(found some problem, it is seemed like a bug), we prepare to deploy it in production network.
another solution is connect ASR1006 to one set of bleaf(9300ex) and ASR1006 is not as a leaf, but this is very difficult to deploy, because we have to have vrf on asr 1006 and bleaf, if we conntect ast1006 directly to spine, we just need config vrf one ASR1006 onetime