Obtained a Homag P110 CNC Router. It was salvaged and I have refurbished.

It is running well on Homag's controller...but I HATE IT! Does not use standard G-code and because it was salvaged Homag service will not support it. How much support does Mach4 have for EtherCAT devices?

At a high level, it has:

Windows PC operating over EtherCAT
PLC - Beckhoff EK1100
Servos - Rexroth / Bosch (Ethercat)
Spindle - Forgot to look...but operating on EtherCAT

I'm sure Craig will get on here and give you a pretty thorough explanation; but for now, in short, Mach4 can run ethercat, but it will be a plugin that you will have to get, and probably have to get the hardware to go along with it. 
Vital Systems has an ethercat card and plugin for Mach4.  Give them a look.  I'm not sure how you can use your existing motors and drives, I have zero experience with ethercat, I just know it is available.
https://www.vitalsystem.com/portal/motion/ethercat/EC01.php

Hi,
there are two ways to run Ethercat with Mach4.

The first is as Cbyrdtopper has suggested, that is to use a VitalSystems board. That means that the PC runs normally but the Vital Systems board is a buffered (with
respect to the trajectory data from the PC) but handles the realtime Ethercat comms.

https://www.automationtechnologiesinc.com/products-page/mach4-ethercat-system/ethercat-motion-controller

The other alternative, and is relatively new, about 18 months or so, is a solution by Kingstar. The idea is that one of the multi-core CPU cores is dedicated as a realtime scheduler.
This is made possible by using RTX software by Interval Zero. This in effect makes your PC genuine realtime. Kingstar have added the software to make the PC an Ethercat master
and the RTX/realtime core provides the Ethercat comms which are by definition realtime.

To my knowledge the only way to buy this solution is to buy a PC, a medium spec ex lease PC probably, that has a high spec Ethernet card fitted, and supplied with the RTX software
and Kingstar software pre installed. The PC and required licenses (think that includes Mach4Hobby) is about $1600USD.

https://www.automationtechnologiesinc.com/products-page/mach4-ethercat-system/cnc-ethercat-motion-control-computer

Check with Smurph, he has had a bit to do with it and was impressed. I understand that the NFS Matsurra mill is set up and running using this Ethercat solution.

Of the two solutions I much prefer the Kingstar/RTX solution.....the Ethercat board has all the limitations and not enough of the benefits of Ethercat

I was very tempted to go this way when designing my new mill. I rather thought the Ethercat solution was beyond my budget, not necessarily overpriced, but just a bit beyond my means.
The other issue is that all the Ethercat hardware commands a premium...which has to be added to the budget. Ethercat would be a fine idea if you had a machine with conveyors, pallet loaders
and all that sort of stuff where you might have 10-15 or more axis motors, but for even a five axis mill existing and cheaper soplutions such as an ESS are adequate.

Craig