There are many reason not to rely on the old sheet vinyl to make a satisfactory base for ceramic or stone tiles. Most would think the main reason not to try this type of installation is the inability to achive a satisfactory bond to the vinyl. With modern mortars, this is no longer a problem, a good bond can be attainable with these special mortars.
I think the main cause of failure is that vinyl flooring will not stay 100% stuck over the entire area for ever. After all. these coverings are installed with water soluble adhesives which can become loose without showing signs that they are loose unless you do some close investigation. More often than not, the desire to just go over vinyl floors is when the substrate is concrete because it's more difficult to remove than if the substrate was wood. Most of these floors are on or below grade which means there is often moisture wicking up which results in a poor bond, and as mentioned before it's sometimes impossible to know if the bond is good or just hanging by a thread.
As for the crack-isolation value, there are many products that are designed for that purpose, and that actually work.
Other reasons not to; The old vinyl should be scarified to get a good bond. Some older vinyl floors contain asbestos and they should not be sanded. Many, perhaps 70-80 % of vinyl floors are too soft and so ceramic over them is a no-no. Most sheets vinyls are not made by the old 'inlaid' method, (hard) rather they are 'printed' and those have a thin foam layer which makes the pattern. Many floors are 12' wide, some 9' wide, those are ALL too soft. The inlaid type come/came no wider than 6' wide.
In addition, some vinyls in the last 20-25 years were installed using the 'perimiflor' method. That is glueing only around the edges and the seams. They appear to be full spread, but they are not.
Having said all that, yes, it is possible, but only if the old is not one of those soft sheet goods. It has to be stuck real good, especially around the edges, and you have to be willing to take a chance that it might fail 20-30 % of the time within a few years, often within the first seasonal cycle.
If you are a tile contractor and want to do it by the book, you'll pass and go to the next job where the people want the work done the way it should be done.