I am afraid this is the only option I can come up with. Everything else will require altering the source .js files generating the widgets' markup, and that would be a serious challenge.
At this time I am not aware of any plans for switching the icons to SVGs but you can submit a feature request at our feedback portal (http://kendoui-feedback.telerik.com/forums/127393-kendo-ui-feedback)
. If the item accumulates enough votes, it will be taken into consideration for future releases.
I can not give you an answer regarding Font Awesome 5 either but if it proves to be very popular and a commonly requested feature by our customers, I am sure there will be information on using it with Kendo UI in some way.