Cursors in PL/pgSQL

Cursors are not supported in PL/pgSQL. I don't see a TODO item to fix
this.

Fixing the syntax to support cursors is easy. The problem then is
that PL/pgSQL uses SPI, and SPI does not support cursors. In spi.c
there is a bit of code for cursor support, with the comment
/* Don't work currently */

Is adding cursor support to SPI a bad idea? Is adding cursor support
to PL/pgSQL undesirable?

Can anybody sketch the problems which would arise when adding cursor
support to SPI?

Thanks.

Ian