HSPA+ is really a stop-gap technology anyway... real world tests are showing that it's not much faster. Most people with good 3G coverage routinely get 3+ mbps on standard HSDPA, which is more than enough speed for the iPad 2. LTE, on the other hand, has other advantages over 3G, not the least of which is greatly reduced latency, which I'd argue is going to be more noticeable than faster throughput.