I've been using some IP from Altera for a DDR2 SDRAM memory controller. I have not been able to get it to work after trying for more than a year and putting in a service request with them. My opinion on that IP and their support of it, to say the least, is that it absolutely stinks!!
Interesting, because the end-user modifications are inherent in the FOSS development model. In other words, it's a psychological expectation problem, not a technical problem---your company is caught between conflicting goals of flexibility and support.
It looks to me that you should get off the fence and decide which business model you're offering: proprietary black box IP provider, or a design services firm that works off a basic, essentially non-proprietary design baseline.
I personally work for an IP developer. One of the biggest problem we face is that our customers change the HDL developed by us on their own without consulting us. But they expect us to do the verification.This delays project delivery..
Same story with Freescale IMX53, the Open-GL graphic IP if from AMD together with the driver.
Without the driver source code it's impossible to switch to a new Linux kernel as nobody can recompile the graphic driver, even at Freescale ! Because of that we had to switch to another processor.
Raspberry Pi is a subsidized product from Broadcom. This is the only way to get this price. It is similar to the BeagleBone from TI. Therefore it is not an open system but a vendor eval board with a new marketing spin.
The biggest problem with IP is that use/knowledge doesn't follow the supplychain. Case in point is the Raspberry PI $35 computer designed for schoolkids to experiment on. There appear to be problems among the USB ports and the built-in USB Ethernet adapter. The problem appears to be in an embedded driver that was licensed to the processor vendor with the UPB/Ethernet IP. Engineers downstream (working for free) of the processor vendor can't reapair the code, because they can't be given access (violation of IP license??). The originator & the licensee can't upgrade without pricing the the processor out of its market.