Yes, you can make IEMs Wireless... With a "Bluetooth Adapter"

 IEMs, or "in-ear monitors", are basically in-ear high-end earphones, that usually look like this:

KZ ZEX hybrid IEM from KZ-Audio

Note the wires. Yes, this has wires. because these are wired IEMs. And most people prefer it that way. In fact, they would even upgrade the wires to monocrystal core, multi-strand, oxygen-free wiring... However, these wires are... replaceable. Yes, you can remove the wires. There are 3 types of plugs, 0.75mm (or 0.78mm), MMCX, and a new one called "S-plug", which seems to be a variation of the 2-pin. 

What if you want a set of wireless IEM? 

You could add on what's commonly called "Bluetooth adapter", or "Bluetooth upgrade wire". And they'd look something like this. This is the split version. You can also get one that's linked together via wire around back of neck. 

KZ AE01 BT 5.4 IEM Adapter via KZ-Audio

See where it connects to the two IEMs? So basically it will turn any 0.75mm or 0.78 mm 2-wire IEM into a Bluetooth wireless version. IEM itself is NOT included, but AE01 itself is available directly from KZ for as low as $25 USD or from Amazon in the US for about $34, which seems to be a bargain. KZ itself also makes a version using several different Qualcomm chipsets for different price points. And you can also find versions made for MMCX and S-plug. 

This obviously, is NOT the only company making such. Prices vary greatly, from $20 to $200. The more expensive ones are from famous maker (such as Shure) and/or using high-end Qualcomm Bluetooth chipset that also support Qualcomm HD audio, AptX, and so on. 

So if you have a good set of 2-wire IEMs, you can turn them wireless with these adapters.