Are you planning on switching them out to can lights later? If so, why not just do it now? It's just as easy to add can lights as it is to hang new pendant lights.

No, it’s an option though. I want to see if I like new pendants first.

ok, in my humble opinion, you have a lot of varied texture and finishes going on. I think between the polished fixture over the nook and the rustic fixtures over the island, your eye will not know where to land if you add another fixture to this space. I would not put two different pendants over the sink area, either keep all the 'kitchen' pendants the same or put to recessed lights over the sink. If it gets too busy it will end up looking like a mish/mosh of lighting. since you seem to have simple clean soft lines through most of your space I would not get carried away with too many lights. also as a side note the fixtures you have now probably give great lighting, the one you are replacing them with will not.

Long and short: if you go with the heavy fixture from progress lighting I would nix the ones over the sink all together. but if you go with something a bit softer you could potentially mix it up a bit, as it is now with the two sizes.

The pendant lights over the island and sink are making the space feel very busy in my opinion. I would have canned lights over these areas to keep it under control.