Are you having trouble with the temperature? If not then there is no need to upgrade, if you feel you are having trouble with the temperature there may be a reason causing this and when you upgrade to the h100 you may still have the problem
a worthy upgrade for any AIO watercooling unit will be the Swiftech H220. A nudge bit more expensive than the H100i, but with quality parts throughout the whole unit(better radiator(copper), better fans(Helix), Better Pump(can power cpu and gpu loop alone), longer tubing, can customize and add blocks/rads/pumps to it. Will come in different tubing color as well(black and white initially). It releases in a couple of days. It will also have a 3x120mm rad variant later.
In general, AIO (All-in-One) or CLC (Closed Loop Coolers, both mean same thing) arent worth it over high end aircooling. A H100i is outperformed by the Noctua NH-D14, which is a good $20-30 cheaper.
Also when you talking the H100i's price (or the Swiftech Dude mentioned), your not far off custom watercooling, an XSPC Raystorm kit is ~$145, cools far better and is upgradable, while a H100 is pretty much just a dead end.
thej difference will end up being in longevity. The swiftech unit is open for modification, and warranty is not void when modified. It can be refilled with the water/coolant of your choice whereas all other AIO loops are sealed permantly uinless you want to forcibly void your warranty, as well as it comes with a 8 4 pin fan header(10$) so you can use multiple fans and control it without needing to buy a new fan controller or splitters, which add onto cost.
the one thing that automatically kills more traditional AIO's in long term use is Galvanic Corrosion. Because Asetek and Coolit AIO's use alluminum for their radiators, it does not bode very well with the copper that is used for block, and can cause corrosion. since the Swiftech unit is entirely copper, the corrosion effect should not happen, at least not in the same time period that traditional AIO's may go into. The point of the Swiftech unit is that its openly modable, and has a pump strong enough that if you wanted to add a gpu block, you could. which is more or less impossible with all other units. Sure, an H100 on sale used is a good value at 55-65. but if you are buying it new the 140$ swiftech unit bundle will be of much greater value than the h100i's 110$
^ Though for $5 more than the H220 is an XSPC Raystorm RS240 kit from FrozenCPU. Comes with a better pump and CPU block with an equivalent rad.
The H220 is expandable yes, but its no replacement for a custom loop. No matter how you cut it, that pump cant be as powerful as the X20 750 V4 in that Raystorm kit, which is only $5 more.
actually, this is where people are slightly misguided. the pump on the h220 is a house made modificaion of the swiftech Apodgee Drive II. the Apodgee Drive 2 does 17.5 liters per minute(1050 liters per hour) wheras the X20 750 does 750 LPH by specification.
in Martin's liquid lab, he tested the H220 directly against the X20 750 where the results are:
edit: I mean AT CES, the H220 tech demo showed that the H220's pump was strong enough to pump a Sandy Bridge E + 2 7970's in Crossfire alone(they added extra radiators, but no extra pumps). This was recorded by Linus
of course, but with an entry kit like the rs240, its on the same lines as the h220 in performance throughout. the pump is known to be strong, and has video footage already of how strong it is. Both pumps have the ability to push 2 gpus ontop of cpus. but lets make a direct price comparison of the pumps:
the X20 750 go for about 65$ the apodgee drive(w/ pump) goes for 145$ for the lga 1155.
Swiftech on OCN noted that the H220 is a modified max wattage version of the MCP35X, a 100$ pump(no res). They also have mentioned that the CPU block has the same thermal layout as teh ADII, which the cpu block on the ADII alone is 70$ for the LGA 1155 vs the raystorms 63$. They are similarly powered and similarly priced. both have distict advantages
the raystorm has a Bay already installed and holds more water, but loses out on if you wanted to add more pumps as a dual 5.25 bay is alot already and adding a pump means one may have to add a standalone pump at the bottom of the case, or change the cpu block.
the h220's distinct advantage is that since it hasnt used a bay yet. you can add a 5.25 bay pump to use in tandem if you wanted to(necessarily dont have to) so adding a new pump would be easier, but loses out on initial reservoir capacity.
the point of the h220 is to bridge AIO and Custom Loops, which is a solid choice.