I don't have a lot of experience of the 12000 routers but from the 12000 Q&A
Q. Is Inter-Switch Link (ISL) or 802.1q encapsulation supported on the Gigabit Ethernet (GE) or Fast Ethernet (FE) Line Cards (LCs)?
A. Cisco IOS Software Release 12.0(6) introduced support for 802.1q on GE interfaces only. 802.1q encapsulation is supported on all the GE LCs. The 12000 Series Internet Router does not support ISL encapsulation, and no support is planned.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...