Lower costs won't help when other solutions are seen as cheaper in labor costs, or as the market leader.
The time needed to invest in imaging with zfd\zcm, when you need to create new images often, could be seen as one point that balances the migration costs.
Since zcm is fundamentally different than zfd, the migration argument can backfire.
In both cases you would need to change to a different application packaging format and your competitors can convert nal packages too.
Competitors products have more visibility in the market and will probably claim that their products are easier to integrate and support, which will save money in the longer term.
What are your plans for application virtualization and will you deliver on that? Competitors deliver now.
All in all you need to polish zcm some more and go into attack mode. This kind of defense will only slowly erode your remaining customer base in my opinion.