This can be achieved today, by writing client side code. Here's sample code:



// Wait for Chat widget to load completely
window.addEventListener("lcw:ready", function handleLivechatReadyEvent(){
var timeToWaitBeforeOfferingProactiveChatInMilliseconds = 20000;//time to wait before Offering proactive chat to web page visitor
// Setting context variables
Microsoft.Omnichannel.LiveChatWidget.SDK.setContextProvider(function contextProvider(){
return {
'Proactive Chat':{'value':'True','isDisplayable':true},
'Time On Page':{'value': timeToWaitBeforeOfferingProactiveChatInMilliseconds ,'isDisplayable':true},
'Page URL':{'value': window.location.href,'isDisplayable':true},
};
});

//Display proactive chat invite after 'timeToWaitBeforeOfferingProactiveChatInMilliseconds' milliseconds
setTimeout(function(){
Microsoft.Omnichannel.LiveChatWidget.SDK.startProactiveChat({message: "Hello! This is a custom proactive messge that I made up."}, false)
},timeToWaitBeforeOfferingProactiveChatInMilliseconds);
});


More details: https://docs.microsoft.com/en-us/dynamics365/customer-service/start-proactive-chat