You can create upto 4294967295 subinterfaces. However maximum limit for VLAN is 4000 per interface, total of 16000 VLANs per router.
http://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k_r4-3/lxvpn/configuration/guide/lesc43xbook/lesc43lbun.html
http://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k_r4-2/interfaces/configuration/guide/hc42asr9kbook/hc42pos.html
