From an economic perspective, using a service like Pivotal feels like placing a bet that the pricing difference between cloud providers will be higher that the cost of paying for Pivotal's support plan (I know, open source, but if you reach a scale where these things matter enough that you care about the cost to switch clouds you are probably at the scale where you find yourself paying for Redhat and etc support plans).

As cool as "cloud agnostic" sounds, paying any real tax to achieve it probably exceeds the long term price differential between major cloud providers. The major clouds sell commodities, recognize that they sell commodities, and they operate as low margin large scale providers. Over time the pricing differences have to average out to about zero, otherwise the market would abandon the always-more-TCO-costly provider (which would cause them to lower their margins to recapture the higher total earnings).