In regards to what new technologies may come about, I do think that many people too often forget about artillery in favour of "flashy" things like Tanks, SMGs or Aircraft. If WW1 is delayed, we could see a lot of more modern and capable artillery introduced by a couple of nations, with France and especially Austria-Hungary getting some new artillery pieces in service. A-H was planning a substantial artillery modernization and reorganization before war began, and they would have extremely modern artillery pieces at their disposal, in large numbers, with 170+ guns per Corps planned, unless I am mistaken. Artillery tractors would also start to make their appearance, making the artillery much more mobile, then it was during the early years of WW1, even Heavy (150+mm) pieces, substantially reducing the number of horses (and men) in artillery service. In general we could see motorization to a greater extent, although mostly confined to supporting branches, not used to motorize combat troops, but motorizing artillery, medical and logistic services.
We could also see aircraft see some further development, but I would say that any development would be more directed towards air reconaissance and artillery spotting, then towards bombing. So more like a replacement for the cavalry, in its scouting purposes, then going for pure combat roles, for which they have not yet proven themselves to be actually useful for.
Horse Cavalry is likely to remain as is, though, I would say that it is a certainty that Lance and Saber are going to be abandoned for good the later the war is delayed. All cavalry that remains is likely to be employed as Dragoons, with their primary roles being recon and serving as mobile reserve of sorts. Perhaps we could see some efforts in motorizatioin being made, by procuring Armored Cars or Motorcycles with Sidecars, to compliment the Horse Cavalry, not replace it entirely.
TBC...
EDIT: Rifles are likely going to remain the same, with perhaps some trend towards shortening the rifles into "Short Rifles", similar to SMLE or Springfield 1903 rifles. Some nations are going to change their rifles/cartridges, with Britain and Austria-Hungary two most likely nations to do so, with Britain going for well known P14 rifle and its .276 Enfield, while Austria-Hungary was trialling 4 different rifles in 1913/14 period, aiming to replace its Mannlicher M95 Straight Pull rifles and their 8x50R, rimmed round nosed cartridge. French "may" end up with semi-automatic, they did play around with the concept before WW1, but without the pressures of war, I do not know that there will be both the will and the funding availlable to do something like that.
MGs are going to remain the same ones that served during WW1, so generally Watercooled Maxims and its derivatives, with some outliers as well, like French Hotchkiss aircooled MG or Austro-Hungarian Schwarzlose MG, with delayed blowback operation. LMGs could make their appearance as well, Lewis was a prewar design, as was Madsen LMG, but to what extent we will see them adopted I am not sure. Perhaps they will remain out of reach of infantry, being issued to cavalry, in an effort to increase their firepower, since they are too expensive for peacetime budgets to handle, to be produced and issued to all of infantry. Mortars were worked on by Germans before WW1, so we are likely to see them in service, although first generation may end up looking a lot like German wheeled mortars of WW1, unlike more familiar and modern looking Stokes types.
Thoughts?