VISA handles 150 000 000 transactions a day.
http://corporate.visa.com/about-visa/technology/transaction-processing.shtml with 86 400 seconds per day, that is 1 739 transactions per second. But we also have to count for other credit cards, bank transfers and a new kinds of transactions that we do not have today, such as micro payments for bloggers, filmmakers etc.
Let us assume roughly 10 000 transaction a second is needed for a viable world crypto currency. Of course not, one single coin will dominate all payments, but let us say that the biggest have 10% stake and hence BTC has to be able to handle 1 000 transactions a seconds. The closer BTC or an Altcoin is to be able to handle this transaction volume, the bigger potential it has to grow to one of the most dominant ones.
With a block generation of 10min, 1MB harcoded blocksize and 400byte transaction size, BTC will never be close to handle the requiered transaction volume. Is there any "fixes" down the road for this, or will an altcoin have to adjust for a satisfying transaction volume?
The block size limit will probably increase a little - maybe 10x. ...but yes, your analysis is essentially correct. There are also methods for block chain merging (like what Ethereum plans on using) which might bring block times in to 1-2 minutes, but essentially we'll never be able to process the number of transactions that the existing finance world does. ...unless we take a different approach and *really* fragment the block chain.
This is only one of several fundamental flaws in some of the "to the moon" rhetoric.