Suppose you take a cruiser handlebar:
And attach drop bar-ends like these to the middle section:
What are the problems that might arise? Assume this is for touring long distances.
I guess there are no ready answers when you choose the path of alt-bars. Experimentation should decide. Consider aspects of comfort and safety.
Comfort — will it be comfortable to use? Cruiser handlebars are beneficial in certain situations (upright position, low speeds). Drops handlebars are beneficial in another, non-intersecting range of situations: low aero position, higher speeds. Will you find yourself in both situations often enough to warrant having both handlebars available to you?
Safety can be roughly split into steering safety and braking safety.
Answering the "comfort" part is a personal matter, I think. The steering part is hard to answer without seeing the frame and knowing the dimensions/geometry of the end result. The braking part is mentioned in the comments, and some of the concerns may be addressed by installing a secondary pair of brake levers.
I agree with Grigory's answer. Some other points to consider:
Clip-on drop bars are meant to be used with mountain-bike bars that are basically straight (they're straight to the point of installation). If you want to go this route, maybe use flat bars, or consider trekking bars for a relatively upright position with more hand placement options.
Cruiser bars are not meant for distance riding, and I doubt that the cruiser-bar position would be effective or comfortable at all.
Drop bar ends try to simulate Drop Handlebars. Drop handlebars and cruiser handlebars are practically oposite ends of a spectrum. Often times trying to obtain benefits of two oposites brings along having both drawbacks too.
Besides riding positions far away from reaching brake and shift levers, a potential problem of adding extensions to handlebars are the extensions hitting or snagging on unexpected parts of the frame or your body.
I have tried some weird accessory combinations and had relative success with a thing similar to bullhorn bars with the bakes and shifters mounted on "upwards" bar extensions at the end of straight handlebars, wrapped with handlebar tape. The width of the contraption was the same as my shoulder's, that made it narrow for urban riding and not wide for high-ish speed riding. My main hand position was in the "upwards" which where on a "middle" position (Not too high to ride upright, not as low as to cause discomfort on long rides. The position was similar to riding "on the hoods" of a regular road handlebar). The short stem used did put the straight part of the handlebar in a somewhat resting position, which I used when riding slow. It allowed for a more upright position. The setup was successful on urban environment working as a delivery guy and on road riding 4+ hours per stage (not road racing, more like touring)
I did all of that because I only had MTBs and MTB parts available, but I'm sure a proper drop handlebar of the proper width, and adjusted at the proper height would have been more straightforward, and more important, would have provided the main benefit of drop handlebars for long rides: three proper, well established, safe and comfortable hand positions.
So my recommendation is to check whether the budget for the proposed extensions could be better spent on a compatible drop bar or bullhorn bar that may yield better overall results. A proper stem that places the handlebar in the correct position is key too.
However, here are a couple of articles that may give you some extra ideas: https://www.sheldonbrown.com/deakins/handlebars.html https://www.sheldonbrown.com/org/thorn-index.html