As per SrimadBhagawat Purana, the 10th avatara of Vishnu will take place as Kali. The time, place, and family are already mentioned. So, there is no chance of Lord Vishnu appearing anywhere else.

शम्भल ग्राम मुख्यस्य ब्राह्मणस्य महात्मनः।
भवने विष्णुयशसः कल्किः प्रादुर्भविष्यति।।
Srimad Bhagavata Maha Purana – 12:2:18

Lord Kalki will appear in the home of the most eminent brahmana of Shambhala village, the great souls Vishnuyasha and his wife, the pure of thought Sumati.

द्वादश्यां शुक्ल-पक्षस्य माधवे मासि माधवम्।
जातं ददृशतुः पुत्रं पितरौ हृष्ट-मानसौ।। (1:2:15 Kalki Purna)

12th of the first part of the moon cycle in the month of Chaitra (March/April, Hindu new year) Lord Krishna (as Kalki) arrived then the father was mentally overwhelmed by the son being born.

This also points to the sun sign of Aries. In Chaitra month, the fifteen days in Shukla paksha (first fortnight / first half of the month) are dedicated to fifteen gods or deities. Each day of the Chaitra month is dedicated to a different god. The 12th day (Chaitra Dwadashi) is dedicated to Lord Sri Maha Vishnu.
http://en.wikipedia.org/wiki/Kalki#Birth