Hi,
I am not sure of the point of that mdev. First, arrays are not table functions. Arrays are data structures. A table function can certainly return all the items in an array data structure as rows (which would be part of #820) but that doesn't mean that a table function could replace an ARRAY data type. Arrays also have to be able to be passed to stored routines and stored in tables too, or they are virtually useless.
Second, WL#820, which far precedes that mdev, adds real table functions without magic "pretend" storage engine as suggested in the later mdev. In any case, you can't return an array or table, from a UDF, without changing the UDF interface which will break other UDF. The UDF interface IS NOT VERSIONED.
wl#820 adds external stored procedures and doesn't modify the udf interface (UDF can rot) The mysql bug link I sent makes item functions internally pluggable, so they could support table functions as well and provide a replacement for UDF. Add an ARRAY data type and implement these patches (which are from Antony Curtis) and you'll get what you want.
It would be a real shame to replace wl#820 work with some half-backed UDF that has not access to internals.
--Justin