i dont think we will see a drop in uploads. like you said, if people will stop uploading for that reason alone then they arent as dedicated as we are and wont be really noticed as a mass contributor to the site 
ran some numbers a while back,
we have 11,500 some registered members.
take the top 10 uploaders and we have 16,000+ uploads between them. thats half the site right there.
take the top 20, 64% of the sites images.
point being those who upload alot wont be effected by this, and as we can see, most of the sites images will continue to be uploaded by these 20 people.
and as for the site growing, if a new member registers and wants to upload 1000 images then they will just learn the rules set down before them and upload those images. no problems. i dont think we get enough images from people who dont read the forums to warrant concern for the sites growth. and this is all assuming that this change will cause people to stop uploading when in fact they will probably just be like "o ya" and continue uploading like normal.
(and if they do stop uploading then maybe we can keep that queue below 1k images lol)