The three in one visa will certainly be a plus for tourists. The time they spend in checkpoints will be reduced. There will be less queues on the border offices.
If a foreign tourist's intention was to visit all three countries, they would pay significantly more in each checkpoint between the three countries. The consolidated fee of 100$ is cheaper that the total accumulation of individual state charges which would amount to about 130$.
The three EAC countries will now be compelled to work together to encourage tourists to visit other countries as well. More awareness of tourism sites in East Africa will arise. While visiting the Mara in Kenya for example, you will be encouraged to use your visa to see the Bujagali falls in Uganda as well. Because countries will no longer compete, there will be an increase in awareness of more touristic sites.
Rwanda, Uganda and Kenya will definitely have no choice but to foster seamless tourism services. This move will definitely charge the governments to improve on their transport systems. Roads will be improved. The railway systems will be revived and as a result tourism will be improved.
The three EAC countries will definitely ensure that they offer quality services like that of their partner states. Nobody wants their client to have a great time in Uganda and Rwanda then only to have poor service in Kenya. I believe the quality of tourism, especially customer service, in the destinations will improve.
With no mention and intention to ban the separate visas of the three different countries, foreign tourists need not fear if all they want is to lie in the sun in Diani beach and return home. The option of the single visa however does increase their choice of destinations. Whichever country they jet into, they have the liberty to traverse the borders within the 90 days of the visa life.