I would like to see the "Units" field in the Item Configuration to support Value Mappings. This would be useful for SNMP-based templates, especially when using item prototypes.
Currently, the "Units" field can be filled with a fixed value or through a macro. While the latter is very useful for sensor units obtained from an SNMP table in Item Prototypes, many SNMP agents (and their vendors) tend to externalize the real unit (say "RPM" for fan speed, "°C" for temperature, "%" for humidity and so on) to an SNMP OID enum, which then must be dereferenced.
For "normal" values, this can be done through value mappings. For the "Units" field, this is currently not supported, and it makes writing (and especially auto-generating) templates from SNMP MIBs or Windows PDH counters very hard.
As such, it would be cool if you could make this happen.