NDVI is an interest of mine as well... unfortunately there is currently nothing that will realistically work with the Plus or the H. Yes, the lens in each camera can be removed... and an appropriate NIR filter installed directly in front of the sensor. However, that does necessitate investing in an additional dedicated camera. Peau Productions has NDVI Blue 446nm + NIR 800nm filters that will work with the CGO3 camera series. There is no indication currently on their site if a filter for the E90/C23 will be added.
However with no Yuneec approved 3rd party apps, there is no mapping app available. Mapping is a supported function of the 520. DroneDeploy (and virtually all apps out there), are DJI compatible only... little support for other platforms. If a version of Tuna's UAV Toolbox for the H Plus with mapping capabilities is developed in the future, that would be another option.
All of this is before you even invest in the NDVI analysis software, which is not cheap.
Last I really looked at it, the initial investment will be $5000 to $7000... and the hardware will not be Yuneec.