Thoughts on my theory that Ireland ITTL becomes a problem because continuing the war without any hope of victory will be seen as a pretext for continued foot-dragging on Home Rule implementation?
Predicates.
1. The Home Rule issue is complicated and was heading towards a civil war in 1914 before events in Sarajevo and elsewhere saved the day.
2. The Irish Parliamentary Party (far and away the largest political faction in southern Ireland in the period) were
generally supportive of the war, on the understanding that this would lead to an all-Ireland state with autonomy within the UK. This support extended to
most of the populace (e.g. the IVF/NVF split)
3. "Home Rule" in 1914 was not independence. It was legislative autonomy within the United Kingdom. This was acceptable to most, with many considering this a step towards full independence.
So let us postulate the Central Powers achieve a quick victory in 1914. Now this will almost certainly require
several divergences from history as we know it. Perhaps Essen does attack Sweden , Gibbs McAdoo was killed at Depot Street, Churchill was killed at Sidney Street and the Haldane Reforms are screwed up, leaving the UK somewhat unable to intervene in mainland Europe 1914.
So Germany knocks out France, perhaps following the original plan and letting the French bleed themselves, followed by a thrust at Paris that works. The rail network is severed, the coal and iron fields are taken, and the Germans take the channel ports before there's a significant UK presence. France will sue for peace and the war ends early in 1915 (I used a variation on this in my EDCverse).
Does the UK continue to fight the war? Well the terrifying prospect of a German controlled continent faces them. But what can they do? An invasion of France (or Germany) seems utterly impossible. There will be a vast Invasion Scare, far worse than previously, and the army will be deployed defensively. The RN may engage in a blockade and/or commerce raiding but that seems unlikely to work (especially given the state of the US economy given my divergence points) but this looks like a losing tactic. They may continue to support Russia, but given the available forces after France is knocked-out of the war that empire is probably doomed also.
Also remember this isn't 1918, the war has ended (as many expected) quickly. Yes there are many, many, dead but not the levels of four years later. Peace settlements can probably be found.
If the UK ends the war then Ireland will be restive. There will be a rapid diminution in support. The war is over and there are other matters to deal with. I could see a form of partition enacted (on a "temporary" basis) with a four county NI state created, perhaps with it's own parliament. Sans the Nine Days Insurrection and the Anglo-Irish War there won't be as much support for the NI state within the rest of the UK. Worst case scenario is open warfare in NEU with "involuntary population movements".
The later implications are fascinating. Will there be a RotPA18 analogue? Will the Labour party's rise be delayed? Will this contribute to revolutionary fervour? The situation will not be as bad as 1918-19 when historically Britain faced large scale unrest and the prospect of revolution but the stresses are still there.
In this case I suspect there will be extensive German interest in Ireland for the next war, preparations for which will begin a couple of days after an armistice is signed.
If the UK continued the war then Ireland will also be restive, there will be a rapid diminution in support. The war is effectively over and there are other matters to deal with. Germany may well attempt to meddle, for basing opportunities at least. I can see a naval war, with raiding and colonial actions, continuing. However I can also see Germany meddling in restive British colonies, necessitating troop deployments around the world. Eventually this will probably peter out. Might there be a Kalterkrieg of sorts as Germany reorganises Europe and everyone prepares for the Next Great War?
As for a German invasion of the UK, frankly this is pretty ludicrous. Barring the nullification of the RN the idea of an opposed landing on such a scale will be rapidly discarded.