SAP has a new on-demand plan.

First of all it’s for the large enterprise, its existing customers, not the mid-market it’s been lackadaisically offering its never-completely-released isolated-tenancy on-demand ERP widgetry, ByDesign.

Second, on-demand is suddenly “the next big evolution” in IT, soliciting the company’s “full commitment.”

According to SAP EVP, large enterprise on-demand John Wookey, the ex-head of Oracle’s application development hired in November, it’s supposed to consist of function-specific applications, available for a presumably low-margin subscription, that plug into the customer’s SAP Business Suite ERP or SCM software and inherit its policy settings.

The multi-tenant architecture, a software-plus-services approach like Microsoft’s, is supposed to avoid the data sharing and integration issues that pop up when dealing with disparate best-of-breed SaaS applications.

Wookey said the widgetry would be powered by the Java-based Frictionless platform SAP got when it bought Florida’s Frictionless Commerce three years ago.

SAP’s already got CRM on-demand, e-sourcing on-demand and cap-and-trade software through its acquisition of Clear Standards last month.

It expects to launch expense management software the middle of next year; the e-sourcing widgetry will be turned into a plug-in and the CRM stuff needs to go multi-tenant.

It’s also got SkyData, a shiny new mobile social CRM acquisition, and a BusinessObjects on-demand portfolio to grow on.

It may make other acquisition to further its goals. It’s proposing that third-party developers eventually develop for the system